Thin-layer-covered golf ball with improved velocity

ABSTRACT

A golf ball comprising a center comprising a polybutadiene having a molecular weight of greater than 200,000 and a resilience index of at least about 40; and a cover layer comprising a polyurethane composition formed from a prepolymer having no greater than 7.5 percent by weight unreacted isocyanate groups.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of co-pendingapplication Nos. 09/311,591, filed May 14, 1999, and 09/461,736, filedDec. 16, 1999.

FIELD OF THE INVENTION

[0002] The invention relates generally to golf balls and, morespecifically, to golf balls with covers formed of a polymer blendcomprising a polyurethane composition and cores formed of apolybutadiene composition. The polyurethane composition comprises aprepolymer of a polyisocyanate and a polyol, and a diamine curing agent.The polybutadiene composition comprises a butadiene polymer with aresilience index greater than about 40 and a molecular greater thanabout 200,000. The golf balls of the present invention have been foundto provide improved velocity.

BACKGROUND OF THE INVENTION

[0003] Conventional golf balls can be divided into several generalclasses: (a) solid golf balls having one or more layers, and (b) woundgolf balls. Solid golf balls include one-piece balls, which are easy toconstruct and relatively inexpensive, but have poor playingcharacteristics and are thus generally limited for use as range balls.Two-piece balls are constructed with a generally solid core and a coverand are generally the most popular with recreational golfers becausethey are very durable and provide maximum distance. Balls having atwo-piece construction are commonly formed of a polymeric core encasedby a cover. Typically, the core is formed from polybutadiene that ischemically crosslinked with zinc diacrylate and/or other similarcrosslinking agents. These balls are generally easy to manufacture, butare regarded as having limited playing characteristics. Solid golf ballsalso include multi-layer golf balls that are comprised of a solid coreof one or more layers and/or a cover of one or more layers. These ballsare regarded as having an extended range of playing characteristics.

[0004] Wound golf balls are generally preferred by many players due totheir high spin and soft “feel” characteristics. Wound golf ballstypically include a solid, hollow, or fluid-filled center, surrounded bya tensioned elastomeric material and a cover. Wound balls generally aremore difficult and expensive to manufacture than solid two-piece balls.

[0005] A variety of golf balls have been designed by manufacturers toprovide a wide range of playing characteristics, such as compression,velocity, “feel,” and spin. These characteristics can be optimized forvarious playing abilities. One of the most common components thatmanufacturers have addresses for optimizing and/or altering the playingcharacteristics of golf balls, is the polymer components present inmodern golf ball construction, in particular, golf ball centers and/orcore. In addition to ionomers, one of the most common polymers employedis polybutadiene and, more specifically, polybutadiene having a highcis-isomer concentration.

[0006] The use of a polybutadiene having a high cis-concentrationresults in a very resilient and rigid golf ball, especially when coupledwith a hard cover material. These highly resilient golf balls have arelatively hard “feel” when struck by a club. Soft “feel” golf ballsconstructed with a high cis-polybutadiene have low resilience. In aneffort to provide improved golf balls, various other polybutadieneformulations have been prepared, as discussed below.

[0007] U.S. Pat. No. 3,239,228 discloses a solid golf ball having a coremolded of polybutadiene rubber with a high sulfur content, and a cover.The polybutadiene content of the core is stereo-controlled to theconfiguration 25-100 percent cis- and 0-65 percenttrans-1,4-polybutadiene, with any remainder having a vinyl configurationof polybutadiene. A preferred embodiment of the polybutadiene golf ballcore contains 35 percent cis-, 52 percent trans-, and 13 percentvinyl-polybutadiene. The level of trans- and vinyl-content are disclosedto be unimportant to the overall playing characteristics of the polymerblend.

[0008] British Patent No. 1,168,609 discloses a molding composition fromwhich improved golf ball cores can be molded and which containscis-polybutadiene as a basic polymer component. The core polymercomponent typically includes at least 60 percent cis-polybutadiene, withthe remainder being either the trans- or vinyl-forms of polybutadiene.In a preferred embodiment, the core polybutadiene component contains 90percent cis-configuration, with the remaining 10 percent being eitherthe trans- or vinyl-configurations of 1,4-polybutadiene.

[0009] U.S. Pat. Nos. 3,572,721 and 3,572,722 disclose a solid, one- ortwo-piece golf ball, with the two-piece ball having a core and a cover.The cover material can include any one of a number of materials, orblends thereof, known to those of ordinary skill in the art, includingtrans-polybutadiene which may be present in an amount from at least 90percent, with the remainder being the cis- and/or vinyl configuration.

[0010] British Patent No. 1,209,032 discloses a two- or three-piece golfball having a core and a cover. The core or cover material can be anymaterial capable of being crosslinked. In particular, the material canbe a polymer or a copolymer of butadiene or isoprene. Preferably, thepolymer component is polybutadiene having a cis content of greater than50 percent by weight.

[0011] U.S. Pat. No. 3,992,014 discloses a one-piece, solid golf ball.The golf ball material is typically polybutadiene, with astereo-configuration selected to be at least 60 percentcis-polybutadiene, with the remaining 40 percent being thetrans-polybutadiene and/or 1,2-polybutadiene (vinyl) isomers.

[0012] U.S. Pat. No. 4,692,497 discloses a golf ball and materialthereof formed by curing a diene polymer including polybutadiene and ametal salt of an alpha, beta ethylenically unsaturated acid using atleast two free radical initiators.

[0013] U.S. Pat. No. 4,931,376 discloses a process for producingbutadiene polymers for use in various applications, including golf ballcover materials. One embodiment of the invention employs a blendedpolymeric resin material, including at least 30 percent by weight of atrans-polybutadiene polymer as a golf ball cover on a two-piece ball. Ina preferred embodiment, the golf ball cover material contains a blendincluding 30 to 90 percent by weight of a trans-polybutadiene polymer.

[0014] U.S. Pat. No. 4,971,329 discloses a solid golf ball made from apolybutadiene admixture of cis-1,4 polybutadiene and 1,2 polybutadiene,a metal salt of an unsaturated carboxylic acid, an inorganic filler, anda free radical initiator. The admixture has about 99.5 percent to about95 percent by weight of cis-1,4 polybutadiene and about 0.5 percent toabout 5 percent by weight of 1,2 polybutadiene.

[0015] U.S. Pat. No. 5,252,652 discloses a one-piece or multi-layeredgolf ball core with improved flying performance from a rubbercomposition comprising a base rubber, preferably 1,4-polybutadiene witha cis-content of at least 40 mole percent, an unsaturated carboxylicacid metal salt, an organic peroxide, and an organic sulfur compoundand/or a metal salt thereof. The organic sulfur compound and/or a metalsalt is typically present in an amount from about 0.05 to 2 parts perhundred by weight and the organic peroxide is typically present in anamount from about 0.5 to 3 parts per hundred by weight of the totalpolymer component.

[0016] European Patent No. 0 577 058 discloses a golf ball containing acore and a cover that is formed as two separate layers. The inner layerof the cover is molded over the core and is formed from ionomer resin.The outer layer of the cover is molded over the inner layer and isformed from a blend of natural or synthetic balata and a crosslinkableelastomer, such as polybutadiene. In one embodiment of the outer layerof the cover, the elastomer is 1,4-polybutadiene having a cis-structureof at least 40 percent, with the remaining 60 percent being thetrans-isomer. A preferred embodiment contains a cis-structure of atleast 90 percent and more preferably, a cis-structure of at least 95percent.

[0017] U.S. Pat. No. 5,421,580 discloses a wound golfball having aliquid center contained in a center bag, a rubber thread layer formed onthe liquid center, and a cover over the wound layer and liquid center.The cover material can include any one of a number of materials, orblends thereof, known to those of ordinary skill in the art, includingtrans-polybutadiene and/or 1,2-polybutadiene (vinyl), such that thecover has a JIS-C hardness of 70-85; preferred trans-percentages are notdisclosed.

[0018] U.S. Pat. No. 5,697,856 discloses a solid golf ball having a coreand a cover wherein the core is produced by vulcanizing a base rubbercomposition containing a butadiene rubber having a cis-polybutadienestructure content of not less than 90 percent before vulcanization. Theamount of trans-polybutadiene structure present after vulcanization is10 to 30 percent, as amounts over 30 percent are alleged todetrimentally result in cores that are too soft with deterioratedresilience performance, and to cause a decrease in golf ballperformance. The core includes a vulcanizing agent, a filler, an organicperoxide, and an organosulfur compound.

[0019] British Patent No. 2,321,021 discloses a solid golf ball having acore and a cover formed on the core and having a two-layered coverconstruction having an inner cover layer and an outer cover layer. Theouter cover layer is comprised of a rubber composite that contains 0.05to 5 parts by weight of an organic sulfide compound. The core rubbercomposition comprises a base rubber, preferably 1,4-polybutadiene havinga cis-content of at least 40 percent by weight, a crosslinking agent, aco-crosslinking agent, an organic sulfide, and a filler. Thecrosslinking agent is typically an organic peroxide present in an amountfrom 0.3 to 5.0 parts by weight and the co-crosslinking agent istypically a metal salt of an unsaturated fatty acid present in an amountfrom 10 to 40 parts by weight. The organic sulfide compound is typicallypresent from 0.05 to 5 parts by weight.

[0020] U.S. Pat. No. 5,816,944 discloses a solid golf ball having a coreand a cover wherein the core has a JIS-C hardness of 50 to 80 and thecover has a Shore-D hardness of 50 to 60. The core material includesvulcanized rubber, such as cis-polybutadiene, with a crosslinker, anorganic peroxide, an organosulfur compound and/or a metal-containingorganosulfur compound, and a filler.

[0021] Additionally, conventional polymers that have a high percentageof the trans-polybutadiene conformation, such as DIENE 35NF, fromFirestone Corp., that has 40 percent cis-isomer and 50 percenttrans-polybutadiene isomer, and mixtures of high-cis- andhigh-trans-polybutadiene isomers, such as CARIFLEX BR1220, from ShellCorporation, and FUREN 88, from Asahi Chemical Co., respectively,typically do not yield high resilience values and therefore are notdesirable.

[0022] In addition to changing center or core ingredients to affect golfball performance characteristics, a number of patents have issued thatare directed towards modifying the propel-ties of layers and covers usedin forming a variety of golf balls, such as wound balls, conventionalsolid balls, multi-layer balls having dual cover layers, dual corelayers, and/or balls having a mantle layer disposed between the coverand the core. The most common polymers used by manufacturers in golfball layers and covers have been ionomers, such as SURLYN, commerciallyavailable from E. I. DuPont de Nemours and Co., of Wilmington, Del.Recently, however, manufacturers have investigated the used ofalternative polymers, such as polyurethane. For example, U.S. Pat. No.3,147,324 is directed to a method of making a golf ball having apolyurethane cover.

[0023] Polyurethanes have been recognized as useful materials for golfball covers since about 1960. Polyurethane is the product of a reactionbetween a polyurethane prepolymer and a curing agent. The polyurethaneprepolymer is a product formed by a reaction between a polyol and adiisocyanate. The curing agents used previously are typically diaminesor glycols. A catalyst is often employed to promote the reaction betweenthe curing agent and the polyurethane prepolymer.

[0024] Since 1960, various companies have investigated the usefulness ofpolyurethane as a golf ball cover material. U.S. Pat. No. 4,123,061teaches a golf ball made from a polyurethane prepolymer of polyether anda curing agent, such as a trifunctional polyol, a tetrafunctionalpolyol, or a diamine. U.S. Pat. No. 5,334,673 discloses the use of twocategories of polyurethane available on the market, i.e., thermoset andthermoplastic polyurethanes, for forming golf ball covers and, inparticular, thermoset polyurethane covered golf balls made from acomposition of polyurethane prepolymer and a slow-reacting amine curingagent, and/or a difunctional glycol. The first commercially successfulpolyurethane covered golf ball was the Titleist® Professional ball,first released in 1993.

[0025] Unlike SURLYN® or ionomer-covered golf balls, polyurethane golfball covers can be formulated to possess the soft “feel” of balatacovered golf balls. However, golf ball covers made from polyurethanehave not, to date, fully matched SURLYN®-covered golf balls with respectto resilience or the rebound that is a function of the initial velocityof a golf ball after impact with a golf club.

[0026] U.S. Pat. No. 3,989,568 discloses a three-component systememploying either one or two polyurethane prepolymers and one or twopolyols or fast-reacting diamine curing agents. The reactants chosen forthe system must have different rates of reactions within two or morecompeting reactions.

[0027] U.S. Pat. No. 4,123,061 discloses a golf ball made from apolyurethane prepolymer of polyether and a curing agent, such as atrifunctional polyol, a tetrafunctional polyol, or a fast-reactingdiamine curing agent.

[0028] U.S. Pat. No. 5,334,673 discloses a golf ball cover made from acomposition of a polyurethane prepolymer and a slow-reacting polyaminecuring agent and/or a difunctional glycol. Resultant golf balls arefound to have improved shear resistance and cut resistance compared tocovers made from balata or SURLYN®.

[0029] U.S. Pat. No. 5,692,974 discloses methods of using cationicionomers in golf ball cover compositions. Additionally, the patentrelates to golf balls having covers and cores incorporating urethaneionomers. Improved resiliency and initial velocity are achieved by theaddition of an alkylating agent such as t-butyl-chloride which inducesionic interactions in the polyurethane to produce cationic typeionomers.

[0030] International Patent Application WO 98/37929 discloses acomposition for golf ball covers that comprises a blend of adiisocyanate/polyol prepolymer and a curing agent comprising a blend ofa slow-reacting diamine and a fast-reacting diamine. Improved “feel”,playability, and durability characteristics are exhibited.

[0031] Conventional polyurethane elastomers are known to have lowerresiliency than SURLYN® and other ionomer resins. It has now beendiscovered that the use of a polyurethane composition, according to thepresent invention, in forming golf ball cores, intermediate and mantlelayers, and/or covers, can raise the velocity of a golf ball preparedwith the composition: (1) closer to the velocities observed withSURLYN®-covered golf balls; and (2) higher than the velocities exhibitedusing alternative urethane compositions. Additionally, it is desired tocombine polyurethane cover compositions with polybutadiene corematerials, especially those having resilience indices greater than about40. Cores formed of materials such as these have been found to provideexceptional resiliency characteristics without a loss in performancecharacteristics (i.e., decreased compression).

[0032] It is thus desired to prepare golf balls having lowercompression, i.e., a softer ball, while having the same or higherresilience than conventional balls. It is alternatively desired toobtain the same or lower compression while achieving greater resilience.

SUMMARY OF THE INVENTION

[0033] The present invention is directed to a golf ball comprising acenter comprising a polybutadiene having a molecular weight of greaterthan 200,000 and a resilience index of at least about 40; and a coverlayer comprising a polyurethane composition formed from a prepolymerhaving no greater than 7.5 percent by weight unreacted isocyanategroups. Preferably, the resilience index is greater than about 50.

[0034] The prepolymer may include an isocyanate, at least one polyol,and at least one curing agent. Preferably, the isocyanate includes4,4′-diphenylmethane diisocyanate, polymeric 4,4′-diphenylmethanediisocyanate, carbodiimide-modified liquid 4,4′-diplenylmethanediisocyanate, 4,4′-dicyclohexylmethane diisocyanate, p-phenylenediisocyanate, toluene diisocyanate, isophoronediisocyanate,p-methylxylene diisocyanate, m-methylxylene diisocyanate, o-methylxylenediisocyanate, or a mixture thereof. The at least one polyol may includepolyether polyols, hydroxy-terminated polybutadiene, polyester polyols,polycaprolactone polyols, polycarbonate polyols, and mixtures thereof.The curing agent may include a polyamine curing agent, a polyol curingagent, or a mixture thereof. It is preferred, however, that the curingagent is a polyamine curing agent.

[0035] If the polyamine is selected as the curing agent, the polyaminecuring agent may include 3,5-dimethylthio-2,4-toluenediamine and isomersthereof; 3,5-diethyltoluene-2,4-diamine and isomers thereof,4,4′-bis-(sec-butylamino)-diphenylmethane;1,4-bis-(sec-butylamino)-benzene, 4,4′-methylene-bis-(2-chloroaniline);4,4′-methylene-bis-(3-chloro-2,6-diethylaniline); trimethyleneglycol-di-p-aminobenzoate; polytetramethyleneoxide-di-p-aminobenzoate;N,N′-dialkyldiamino diphenyl methane; p, p′-methylene dianiline;phenylenediamine; 4,4′-methylene-bis-(2-chloroaniline);4,4′-methylene-bis-(2,6-diethylaniline);4,4′-diamino-3,3′-diethyl-5,5′-dimethyl diphenylmethane;2,2′,3,3′-tetrachloro diamino diphenylmethane;4,4′-methylene-bis-(3-chloro-2,6-diethylaniline); and mixtures thereof.

[0036] In one embodiment, however, the curing agent is a polyol curingagent. If the curing agent is a polyol, preferably, the polyol curingagent includes ethylene glycol; diethylene glycol; polyethylene glycol;propylene glycol; polypropylene glycol; lower molecular weightpolytetramethylene ether glycol; 1,3-bis(2-hydroxyethoxy)benzene;1,3-bis-[2-(2-hydroxyethoxy)ethoxy]benzene;1,3-bis-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}benzene; 1,4-butanediol;1,5-pentanediol; 1,6-hexanediol; resorcinol-di-(β-hydroxyethyl)ether;hydroquinone-di-(β-hydroxyethyl)ether; trimethylol propane, and mixturesthereof.

[0037] In a another embodiment, the prepolymer has between about 2.5percent and about 7.5 percent by weight unreacted isocyanate groups. Thecover layer preferably has a thickness of less than about 0.05 inches.Further, the center should have a Mooney viscosity of between about 40and about 80 and, preferably, between about 45 and about 60. In apreferred embodiment, the polybutadiene has a vinyl-polybutadiene isomercontent of less than about 2 percent by weight and the polybutadiene hasa cis-isomer content of at least about 95 percent by weight.

[0038] The golf ball center outer diameter is preferably of no less thanabout 1.55 inches and, additionally, the center further includes amaterial formed from a conversion reaction of polybutadiene having afirst amount of trans-polybutadiene, a free radical source, and at leastone cis-to-trans catalyst. Preferably, the reaction occurs at atemperature sufficient to form a polybutadiene reaction product havingan second amount of trans-polybutadienie greater than the first amountof trans-polybutadiene. The cis-to-trans catalyst may include at leastone of a organosulfur component, an inorganic sulfur compound, anaromatic organometallic compound, a metal-organosulfur compound,tellurium, selenium, elemental sulfur, a polymeric sulfur, or anaromatic organic compound. The organosulfur component may include atleast one of 4,4′-diphenyl disulfide, 4,4′-ditolyl disulfide, or2,2′-benzamido diphenyl disulfide. Preferably, the cis-to-trans catalystis present in an amount from about 0.1 to 10 parts per hundred ofpolybutadiene.

[0039] In another embodiment, the golf ball further includes anintermediate layer juxtaposed between the center and the cover layer,wherein the intermediate layer comprises a material formed from aconversion reaction of polybutadiene having a first amount oftrans-polybutadiene, a free radical source, and a cis-to-trans catalystcomprising at least one organosulfur component, wherein the intermediatelayer has an outer diameter of no less than about 1.58 inches, andwherein the center has an outer diameter of less than about 1.55 inches.In yet another embodiment, the cover layer comprises an inner coverlayer and an outer cover layer, the inner cover layer juxtaposed thecenter and the outer cover layer. Preferably, at least one of the innerand outer cover layer has a thickness of less than about 0.05 inches.

[0040] If present, the inner cover layer is formed from at least onematerial selected from the group comprising of an ionomer resin, apolyurethane, a polyetherester, a polyetheramide, a polyester, adynamically vulcanized elastomer, a functionalized styrenebutadieneelastomer, a metallocene polymer, nylon, acrylonitrile butadiene-styrenecopolymer or blends thereof. In still another embodiment, the innercover has an outer diameter of at least about 1.55 inches and,preferably, between about 1.58 and about 1.64 inches. In an additionalembodiment, the polyurethane is a thermoplastic or thermoset material.

[0041] The present invention is also directed to a golf ball comprisinga center comprising a polybutadiene having a molecular weight of greaterthan 300,000 and a resilience index of at least about 40; an outer corelayer having an outer diameter of no less than about 1.51 inches; aninner cover layer surrounding the outer core layer; and an outer coverlayer comprising of a polyurethane composition formed from a prepolymerhaving no greater than about 7.5 percent by weight unreacted isocyanategroups. Preferably, the resilience index is greater than about 50.

[0042] The prepolymer may include an isocyanate, at least one polyol,and at least one curing agent. Preferably, the isocyanate includes4,4′-diphenylmethane diisocyanate, polymeric 4,4′-diphenylmethanediisocyanate, carbodiimide-modified liquid 4,4′-diphenylmethanediisocyanate, 4,4′-dicyclohexylmethane diisocyanate, p-phenylenediisocyanate, toluene diisocyanate, isophoronediisocyanate,p-methylxylene diisocyanate, m-methylxylenie diisocyanate,o-methylxylene diisocyanate, or a mixture thereof. The at least onepolyol may include polyether polyols, hydroxy-terminated polybutadiene,polyester polyols, polycaprolactone polyols, polycarbonate polyols, andmixtures thereof. The curing agent may include a polyamine curing agent,a polyol curing agent, or a mixture thereof. It is preferred, however,that the curing agent is a polyamine curing agent.

[0043] If the polyamine is selected as the curing agent, the polyaminecuring agent may include 3,5-dimethylthio-2,4-toluenediamine and isomersthereof; 3,5-diethyltoluene-2,4-diamine and isomers thereof;4,4′-bis-(sec-butylamino)-diphenylmethane;1,4-bis-(sec-butylamino)-benzene, 4,4′-methylene-bis-(2-chloroaniline);4,4′-methylene-bis-(3-chloro-2,6-diethylaniline); trimethyleneglycol-di-p-aminobenzoate; polytetramethyleneoxide-di-p-aminobenzoate;N,N′-dialkyldiamino diphenyl methane; p, p′-methylene dianiline;phenylenediamine; 4,4′-methylene-bis-(2-chloroaniline);4,4′-methylene-bis-(2,6-diethylaniline);4,4′-diamino-3,3′-diethyl-5,5′-dimethyl diphenylmethane;2,2′,3,3′-tetrachloro diamino diphenylmethane;4,4′-methylene-bis-(3-chloro-2,6-diethylaniline); and mixtures thereof.

[0044] In one embodiment, however, the curing agent is a polyol curingagent. If the curing agent is a polyol, preferably, the polyol curingagent includes ethylene glycol; diethylene glycol; polyethylene glycol;propylene glycol; polypropylene glycol; lower molecular weightpolytetramethylene ether glycol; 1,3-bis(2-hydroxyethoxy)benzene;1,3-bis-[2-(2-hydroxyethoxy)ethoxy]benzene;1,3-bis-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy)benzene; 1,4-butanediol;1,5-pentanediol; 1,6-hexanediol; resorcinol-di-(-hydroxyethyl)ether;hydroquinone-di-(-hydroxyethyl)ether; trimethylol propane, and mixturesthereof.

[0045] In a another embodiment, the prepolymer has between about 2.5percent and about 7.5 percent by weight unreacted isocyanate groups. Atleast one of the inner and outer cover layers preferably has a thicknessof less than about 0.05 inches. Further, the center should have a Mooneyviscosity of between about 40 and about 80. In a preferred embodiment,the polybutadiene has a vinyl-polybutadiene isomer content of less thanabout 2 percent by weight and the polybutadiene has a cis-isomer contentof at least about 95 percent by weight.

[0046] The golf ball center outer diameter is preferably of no less thanabout 1.55 inches and, additionally, the center further includes amaterial formed from a conversion reaction of polybutadiene having afirst amount of trans-polybutadiene, a free radical source, and at leastone cis-to-trans catalyst. Preferably, the reaction occurs at atemperature sufficient to form a polybutadiene reaction product havingan second amount of trans-polybutadienie greater than the first amountof trans-polybutadiene. The cis-to-trans catalyst may include at leastone of an organosulfur compound, an inorganic sulfur compound, anaromatic organometallic compound, a metal-organosulfur compound,tellurium, selenium, elemental sulfur, a polymeric sulfur, or anaromatic organic compound. The organosulfur component may include atleast one of 4,4′-diphenyl disulfide, 4,4′-ditolyl disulfide, or2,2′-benzamido diphenyl disulfide. Preferably, the cis-to-trans catalystis present in an amount from about 0.1 to 10 parts per hundred ofpolybutadiene.

[0047] In one embodiment, the inner cover layer includes an ionomerresin, a polyurethane, a polyetherester, a polyetheramide, a polyester,a dynamically vulcanized elastomer, a functionalized styrenebutadieneelastomer, a metallocene polymer nylon, acrylonitrile butadiene-styrenecopolymer or blends thereof. The inner cover may have an outer diameterof at least about 1.55 inches and, preferably, between about 1.58 andabout 1.64 inches. In an additional embodiment, the polyurethane is athermoplastic or thermoset material.

[0048] The present invention is also directed to a golf ball comprisinga center formed of a cis-polybutadiene having a molecular weight ofgreater than 300,000 and a resilience index of at least about 40; anouter core layer having an outer diameter of no less than about 1.51inches; an inner cover layer surrounding the outer core layer, the innercover layer comprising a polyurethane; and an outer cover layercomprising an ionomer or an elastomeric material.

[0049] The present invention is also directed to a golf ball comprisinga center comprising a polybutadiene having a molecular weight of greaterthan 300,000 and a resilience index of at least about 40; an outer corelayer having an outer diameter of no less than about 1.51 inches; aninner cover layer surrounding the outer core layer; and an outer coverlayer; wherein the inner and outer cover layers are formed of apolyurethane composition.

BRIEF DESCRIPTION OF THE DRAWINGS

[0050]FIG. 1 is a cross-sectional view of a two-piece golf ball having acover and a core according to the invention;

[0051]FIG. 2 is a cross-section of a golf ball having an intermediatelayer between a cover and a center according to the invention; and

[0052]FIG. 3 is a cross-section of a golf ball having more than oneintermediate layer between a cover and a center according to theinvention.

DEFINITIONS

[0053] The term “about,” as used herein in connection with one or morenumbers or numerical ranges, should be understood to refer to all suchnumbers, including all numbers in a range.

[0054] As used herein, “cis-to-trans catalyst” means any component or acombination thereof that will convert at least a portion ofcis-polybutadiene isomer to trans-polybutadiene isomer at a giventemperature. It should be understood that the combination of thecis-isomer, the trans-isomer, and any vinyl-isomer, measured at anygiven time, comprises 100 percent of the polybutadiene.

[0055] As used herein, the term “active ingredients” is defined as thespecific components of a mixture or blend that are essential to thechemical reaction.

[0056] As used herein, substituted and unsubstituted “aryl” groups meansa hydrocarbon ring bearing a system of conjugated double bonds,typically comprising 4n+2π ring electrons, where n is an integer.Examples of aryl groups include, but are not limited to phenyl,naphthyl, anisyl, tolyl, xylenyl and the like. According to the presentinvention, aryl also includes heteroaryl groups, e.g., pyrimidine orthiophene. These aryl groups may also be substituted with any number ofa variety of functional groups. In addition to the functional groupsdescribed herein in connection with carbocyclic groups, functionalgroups on the aryl groups can include hydroxy and metal salts thereof;mercapto and metal salts thereof; halogen; amino, nitro, cyano, andamido; carboxyl including esters, acids, and metal salts thereof; silyl;acrylates and metal salts thereof; sulfonyl or sulfonamide; andphosphates and phosphites; and a combination thereof.

[0057] As used herein, the term “Atti compression” is defined as thedeflection of an object or material relative to the deflection of acalibrated spring, as measured with an Atti Compression Gauge, that iscommercially available from Atti Engineering Corp. of Union City, N.J.Atti compression is typically used to measure the compression of a golfball. When the Atti Gauge is used to measure cores having a diameter ofless than 1.680 inches, it should be understood that a metallic or othersuitable shim is used to make the measured object 1.680 inches indiameter. However, when referring to the compression of a core, it ispreferred to use a compressive load measurement. The term “compressiveload” is defined as the normalized load in pounds for a 10.8-percentdiametrical deflection for a spherical object having a diameter of 1.58inches.

[0058] As used herein, substituted and unsubstituted “carbocyclic” meanscyclic carbon-containing compounds, including, but not limited tocyclopentyl, cyclohexyl, cycloheptyl, adamantyl, and the like. Suchcyclic groups may also contain various substituents in which one or morehydrogen atoms has been replaced by a functional group Such functionalgroups include those described above, and lower alkyl groups having from1-28 carbon atoms. The cyclic groups of the invention may furthercomprise a heteroatom.

[0059] As used herein, the term “coefficient of restitution” for golfballs is defined as the ratio of the rebound velocity to the inboundvelocity when balls are fired into a rigid plate. The inbound velocityis understood to be 125 ft/s.

[0060] As used herein, the term “dynamic stiffness” is defined as loaddivided by the deflection for a 1.4-mm spherical radius penetrationprobe oscillating at 1 Hz with an amplitude of 100 μm. The probedynamically penetrates the surface of a sample material. Materialsamples of spherical cores were prepared by sectioning out a 6-mm-thicklayer along the equator of core to produce a disk 6 mm thick with onesurface containing the geometric center of the core. By positioning theprobe at any selected radial position on the disk, a dynamic stiffnessmeasurement may be obtained. Accurate dynamic measurements may be madeby keeping the material sample at a substantially uniform temperature.The dynamic stiffness was acquired using a Dynamic Mechanical Analyzer,Model DMA 2980 available from TA Instruments Corporation of New Castle,Del. The instrument setting for the DMA 2980 were 1-Hz frequency, 100-μmamplitude, 0.3-N static load, and auto strain of 105 percent. The 1.4-mmspherical radius probe is available from TA Instruments as a penetrationkit accessory to the DMA 2980. The DMA 2980 is equipped with atemperature-controlled chamber that enables testing at a wide variety ofambient temperatures.

[0061] The method and instrument utilized for measuring “dynamicstiffness” may also be used to measure loss tangent (also commonlyreferred to as tan δ). Loss tangent is the ratio of loss modulus tostorage modulus. Loss modulus is the portion of modulus which is out ofphase with displacement and storage modulus is the portion of moduluswhich is in phase with displacement. The DMA 2980 automaticallycalculates and reports loss tangent.

[0062] As used herein, the terms “Group VIA component” or “Group VIAelement” mean a component that includes a sulfur component, a seleniumcomponent, or a tellurium component, or a combination thereof.

[0063] As used herein, the term “sulfur component” means a componentthat is elemental sulfur, polymeric sulfur, or a combination thereof. Itshould be further understood that “elemental sulfur” refers to the ringstructure of S₈ and that “polymeric sulfur” is a structure including atleast one additional sulfur relative to the elemental sulfur.

[0064] As used herein, the term “fluid” includes a liquid, a paste, agel, a gas, or any combination thereof.

[0065] As used herein, the term “molecular weight” is defined as theabsolute weight average molecular weight. The molecular weight isdetermined by the following method: approximately 20 mg of polymer isdissolved in 10 mL of tetrahydrofuran (“THF”), which may take a few daysat room temperature depending on the polymer's molecular weight anddistribution. One liter of THF is filtered and degassed before beingplaced in a high-performance liquid chromatography (“HPLC”) reservoir.The flow rate of the HPLC is set to 1 mL/min through a Viscogel column.This non-shedding, mixed bed, column model GMH_(HR)-H, which has an IDof 7.8 mm and 300 mm long is available from Viscotek Corp. of Houston,Tex. The THF flow rate is set to 1 mL/min for at least one hour beforesample analysis is begun or until stable detector baselines areachieved. During this purging of the column and detector, the internaltemperature of the Viscotek TDA Model 300 triple detector should be setto 40° C. This detector is also available from Viscotek Corp. The threedetectors (i.e., Refractive Index, Differential Pressure, and LightScattering) and the column should be brought to thermal equilibrium, andthe detectors should be purged and zeroed, to prepare the system forcalibration according to the instructions provided with this equipment.A 100-μL aliquot of sample solution can then be injected into theequipment and the molecular weight of each sample can be calculated withthe Viscotek's triple detector software. When the molecular weight ofthe polybutadiene material is measured, a dn/dc of 0.130 should alwaysbe used. It should be understood that this equipment and these methodsprovide the molecular weight numbers described and claimed herein, andthat other equipment or methods will not necessarily provide equivalentvalues as used herein.

[0066] As used herein, the term “multilayer” means at least two layersand includes liquid center balls, wound balls, hollow-center balls, andballs with at least two intermediate layers and/or an inner or outercover.

[0067] As used herein, the term “parts per hundred,” also known as“phr,” is defined as the number of parts by weight of a particularcomponent present in a mixture, relative to 100 parts by weight of thetotal polymer component. Mathematically, this can be expressed as theweight of an ingredient divided by the total weight of the polymer,multiplied by a factor of 100.

[0068] As used herein, the term “substantially free” means less thanabout 5 weight percent, preferably less than about 3 weight percent,more preferably less than about 1 weight percent, and most preferablyless than about 0.01 weight percent.

[0069] As used herein the term “resilience index” is defined as thedifference in loss tangent measured at 10 cpm and 1000 cpm divided by990 (the frequency span) multiplied by 100,000 (for normalization andunit convenience). The loss tangent is measured using an RPA 2000manufactured by Alpha Technologies of Akron, Ohio. The RPA 2000 is setto sweep from 2.5 to 1000 cpm at a temperature of 100° C. using an arcof 0.5 degrees. An average of six loss tangent measurements wereacquired at each frequency and the average is used in calculation of theresilience index. The computation of resilience index is as follows:

Resilience Index=100,000·[(loss tangent@10 cpm)−(loss tangent@1000cpm)]/990

DETAILED DESCRIPTION OF THE INVENTION

[0070] Referring to FIG. 1, a golf ball 10 of the present invention caninclude a core 12, a cover 16, and optional inner cover layer 16 asurrounding the core 12. Referring to FIG. 2, a golf ball 20 of thepresent invention can include a center 22, a cover 26, an inner coverlayer 26 a, and at least one intermediate layer 24 disposed between thecover and the center. Each of the cover and center may also include morethan one layer; i.e., the golf ball can be a conventional three-piecewound ball, a two-piece ball, a ball having a multi-layer core or anintermediate layer or layers, etc. Thus, referring to FIG. 3, a golfball 30 of the present invention can include a center 32, a cover 38,and intermediate layers 34 and 36 disposed between the cover and thecenter. Although FIG. 3 shows only two intermediate layers, it will beappreciated that any number or type of intermediate layers may be used,as desired.

[0071] The present invention relates to two piece golf balls having acore and a cover, or multilayer golf balls having a solid, hollow, orfluid-filled center, a cover, and at least one intermediate layerdisposed concentrically adjacent to the center. At least one of thecenter or optional intermediate layer includes a reaction product thatincludes a cis-to-trans catalyst, a resilient polymer component havingpolybutadiene, a free radical source, and optionally, a crosslinkingagent, a filler, or both. Preferably, the reaction product has a firstdynamic stiffness measured at −50° C. that is less than about 130percent of a second dynamic stiffness measured at 0° C. More preferably,the first dynamic stiffness is less than about 125 percent of the seconddynamic stiffness. Most preferably, the first dynamic stiffness is lessthan about 110 percent of the second dynamic stiffness.

[0072] The invention also includes a method to convert the cis-isomer ofthe polybutadiene resilient polymer component to the trans-isomer duringa molding cycle and to form a golf ball. Various combinations ofpolymers, cis-to-trans catalysts, fillers, crosslinkers, and a source offree radicals, may be used. To obtain a higher resilience and lowercompression center or intermediate layer, a high-molecular weightpolybutadiene with a cis-isomer content preferably greater than about 90percent is converted to increase the percentage of trans-isomer contentat any point in the golf ball or portion thereof, preferably to increasethe percentage throughout substantially all of the golf ball or portionthereof, during the molding cycle. More preferably, thecis-polybutadiene isomer is present in an amount of greater than about95 percent of the total polybutadiene content. Without wishing to bebound by any particular theory, it is believed that a low amount of1,2-polybutadiene isomer (“vinyl-polybutadiene”) is desired in theinitial polybutadiene, and the reaction product. Typically, the vinylpolybutadiene isomer content is less than about 7 percent. Preferably,the vinyl polybutadiene isomer content is less than about 4 percent.More preferably, the vinyl polybutadiene isomer content is less thanabout 2 percent. Without wishing to be bound by any particular theory,it is also believed that the resulting mobility of the combined cis- andtrans-polybutadiene backbone is responsible for the lower modulus andhigher resilience of the reaction product and golf balls including thesame.

[0073] To produce a polymer reaction product that exhibits the higherresilience and lower modulus (low compression) properties that aredesirable and beneficial to golf ball playing characteristics,high-molecular-weight cis-1,4-polybutadiene, preferably may be convertedto the trans-isomer during the molding cycle. The polybutadiene materialtypically has a molecular weight of greater than about 200,000.Preferably, the polybutadiene molecular weight is greater than about250,000, more preferably between about 300,000 and 500,000. Withoutwishing to be bound by any particular theory, it is believed that thecis-to-trans catalyst component, in conjunction with the free radicalsource, acts to convert a percentage of the polybutadiene polymercomponent from the cis- to the trans-conformation. The cis-to-transconversion requires the presence of a cis-to-trans catalyst, such as anorganosulfur or metal-containing organosulfur compound, a substituted orunsubstituted aromatic organic compound that does not contain sulfur ormetal, an inorganic sulfide compound, an aromatic organometalliccompound, or mixtures thereof. The cis-to-trans catalyst component mayinclude one or more of the other cis-to-trans catalysts describedherein.

[0074] In one embodiment, the at least one organosulfur component issubstantially free of metal, which typically means less than about 10weight percent metal, preferably less than about 3 weight percent metal,more preferably less than about 1 weight percent metal, and mostpreferably only trace amounts of metal, such as less than about 0.01weight percent.

[0075] As used herein when referring to the invention, the term“organosulfur compound(s)” or “organosulfur component(s),” means atleast one of 4,4′-diphenyl disulfide; 4,4′-ditolyl disulfide;2,2′-benzamido diphenyl disulfide; bis(2-aminophenyl) disulfide;bis(4-aminobiphenyl)disulfide; bis(3-aminophenyl)disulfide;2,2′-bis(4-aminonaphthyl)disulfide; 2,2′-bis(3-aminonaphthyl)disulfide;2,2′-bis(4-aminonaphthyl) disulfide; 2,2′-bis(5-aminonaphthyl)disulfide;2,2′-bis(6-aminonaphthyl)disulfide; 2,2′-bis(7-aminonaphthyl)disulfide;2,2′-bis(8-aminonaphthyl)disulfide; 1,1′-bis(2-aminonaphthyl)disulfide;1,1′-bis(3-aminonaphthyl)disulfide; 1,1′-bis(3-aminonaphthyl) disulfide;1,1′-bis(4-aminonaphthyl)disulfide; 1,1′-bis(5-aminonaphthyl)disulfide;1,1′-bis(6-aminonaphthyl)disulfide; 1,1′-bis(7-aminonaphthyl)disulfide;1,1′-bis(8-aminonaphthyl)disulfide;1,2′-diamino-1,2′-dithiodinaphthalene;2,3′-diamino-1,2′-dithiodinaphthalene; bis(4-chlorophenyl)disulfide;bis(2-chlorophenyl)disulfide; bis(3-chlorophenyl)disulfide;bis(4-bromophenyl)disulfide; bis(2-bromophenyl)disulfide;bis(3-bromophenyl)disulfide; bis(4-fluorophenyl)disulfide;bis(4-iodophenyl)disulfide; bis(2,5-dichlorophenyl)disulfide;bis(3,5-dichlorophenyl)disulfide; bis (2,4-dichlorophenyl) disulfide;bis(2,6-dichlorophenyl)disulfide; bis(2,5-dibromophenyl)disulfide;bis(3,5-dibromophenyl)disulfide; bis(2-chloro-5-bromophenyl)disulfide;bis(2,4,6-trichlorophenyl)disulfide;bis(2,3,4,5,6-pentachlorophenyl)disulfide; bis(4-cyanophenyl) disulfide;bis(2-cyanophenyl)disulfide; bis(4-nitrophenyl)disulfide;bis(2-nitrophenyl) disulfide; 2,2′-dithiobenzoic acid ethylester;2,2′-dithiobenzoic acid methylester; 2,2′-dithiobenzoic acid;4,4′-dithiobenzoic acid ethylester; bis(4-acetylphenyl)disulfide;bis(2-acetylphenyl)disulfide; bis(4-formylphenyl)disulfide;bis(4-carbamoylphenyl)disulfide; 1,1′-dinaphthyl disulfide;2,2′-dinaphthyl disulfide; 1,2′-dinaphthyl disulfide;2,2′-bis(1-chlorodinaphthyl)disulfide;2,2′-bis(1-bromonaphthyl)disulfide; 1,1′-bis(2-chloronaphthyl)disulfide; 2,2′-bis(1-cyanonaphtyl)disulfide;2,2′-bis(1-acetylnaphthyl)disulfide; and the like; or a mixture thereof.Preferred organosulfur components include 4,4′-diphenyl disulfide,4,4′-ditolyl disulfide, or 2,2′-benzamido diphenyl disulfide, or amixture thereof. A more preferred organosulfur component includes4,4′-ditolyl disulfide. The organosulfur cis-to-trans catalyst, whenpresent, is preferably present in an amount sufficient to produce thereaction product so as to contain at least about 12 percenttrans-polybutadiene isomer, but typically is greater than about 32percent trans-polybutadiene isomer based on the total resilient polymercomponent. Suitable metal-containing organosulfur components include,but are not limited to, cadmium, copper, lead, and tellurium analogs ofdiethyldithiocarbamate, diamyldithiocarbamate, anddimethyldithiocarbamate, or mixtures thereof Suitable substituted orunsubstituted aromatic organic components that do not include sulfur ora metal include, but are not limited to, 4,4′-diphenyl acetylene,azobenzene, or a mixture thereof. The aromatic organic group preferablyranges in size from C₆ to C₂₀, and more preferably from C₆ to C₁₀.Suitable Inorganic sulfide components include, but are not limited totitanium sulfide, manganese sulfide, and sulfide analogs of iron,calcium, cobalt, molybdenum, tungsten, copper, selenium, yttrium, zinc,tin, and bismuth. The cis-to-trans catalyst may also be a blend of anorganosulfur component and an inorganic sulfide component.

[0076] A substituted or unsubstituted aromatic organic compound may alsobe included in the cis-to-trans catalyst. In one embodiment, thearomatic organic compound is substantially free of metal. Suitablesubstituted or unsubstituted aromatic organic components include, butare not limited to, components having the formula(R₁)_(x)—R₃—M—R₄—(R₂)_(y), wherein R₁ and R₂ are each hydrogen or asubstituted or unsubstituted C₁₋₂₀ linear, branched, or cyclic alkyl,alkoxy, or alkylthio group, or a single, multiple, or fused ring C₆ toC₂₄ aromatic group; x and y are each an integer from 0 to 5; R₃ and R₄are each selected from a single, multiple, or fused ring C₆ to C₂₄aromatic group; and M includes an azo group or a metal component. R₃ andR₄ are each preferably selected from a C₆ to C₁₀ aromatic group, morepreferably selected from phenyl, benzyl, naphthyl, benzamido, andbenzothiazyl. R₁ and R₂ are each preferably selected from a substitutedor unsubstituted C₁₋₁₀ linear, branched, or cyclic alkyl, alkoxy, oralkylthio group or a C₆ to C₁₀ aromatic group. When R₁, R₂, R₃, or R₄,are substituted, the substitution may include one or more of thefollowing substituent groups: hydroxy and metal salts thereof; mercaptoand metal salts thereof; halogen; amino, nitro, cyano, and amido;carboxyl including esters, acids, and metal salts thereof, silyl;acrylates and metal salts thereof; sulfonyl or sulfonamide; andphosphates and phosphites. When M is a metal component, it may be anysuitable elemental metal available to those of ordinary skill in theart. Typically, the metal will be a transition metal, althoughpreferably it is tellurium or selenium.

[0077] The cis-to-trans catalyst can also include a Group VIA component,as defined herein. Elemental sulfur and polymeric sulfur arecommercially available from, e.g., Elastochem, Inc. of Chardon, Ohio.Exemplary sulfur catalyst compounds include PB(RM-S)-80 elemental sulfurand PB(CRST)-65 polymeric sulfur, each of which is available fromElastochem, Inc. An exemplary tellurium catalyst under the tradenameTELLOY and an exemplary selenium catalyst under the tradename VANDEX areeach commercially available from RT Vanderbilt.

[0078] The cis-to-trans catalyst is preferably present in an amount fromabout 0.1 to 10 parts per hundred of the total resilient polymercomponent. More preferably, the cis-to-trans catalyst is present in anamount from about 0.1 to 5 parts per hundred of the total resilientpolymer component. Most preferably, the cis-to-trans catalyst is presentin an amount from about 0.1 to 8 parts per hundred of the totalresilient polymer component. The cis-to-trans catalyst is typicallypresent in an amount sufficient to produce the reaction product so as toincrease the trans-polybutadiene isomer content to contain from about 5percent to 70 percent trans-polybutadiene based on the total resilientpolymer component.

[0079] The measurement of trans-isomer content of polybutadiene referredto herein was and can be accomplished as follows. Calibration standardsare prepared using at least two polybutadiene rubber samples of knowntrans-content, e.g., high and low percent trans-polybutadiene). Thesesamples are used alone and blended together in such a way as to create aladder of trans-polybutadiene content of at least about 1.5% to 50% orto bracket the unknown amount, such that the resulting calibration curvecontains at least about 13 equally spaced points.

[0080] Using a commercially available Fourier Transform Infrared(“FTIR”) spectrometer equipped with a Photoacoustic (“PAS”) cell, a PASspectrum of each standard was obtained using the following instrumentparameters: scan at speed of 2.5 KHz (0.16 cm/s optical velocity), use a1.2 KHz electronic filter, set an undersampling ratio of 2 (number oflaser signal zero crossings before collecting a sample), co-add aminimum of 128 scans at a resolution of 4 cm⁻¹ over a range of 375 to4000 cm⁻¹ with a sensitivity setting of 1.

[0081] The cis-, trans-, and vinyl-polybutadiene peaks are typicallyfound between 600 and 1100 cm⁻¹ in the PAS spectrum. The area under eachof the trans-polybutadiene peaks can be integrated. Determining thefraction of each peak area relative to the total area of the threeisomer peaks allow construction of a calibration curve of thetrans-polybutadiene area fraction versus the actual trans-polybutadienecontent. The correlation coefficient (R²) of the resulting calibrationcurve must be a minimum of 0.95.

[0082] A PAS spectrum is obtained, using the parameters described above,for the unknown core material at the point of interest (e.g., thesurface or center of the core) by filling the PAS cell with a samplecontaining a freshly cut, uncontaminated surface free of foreignmatters, such as mold release and the like. The trans-polybutadiene areafraction of the unknown is analyzed to determine the actual trans-isomercontent from the calibration curve.

[0083] In one known circumstance when barium sulfate is included, theabove method for testing trans-content may be less accurate. Thus, anadditional or alternative test of the trans-content of polybutadiene isas follows. Calibration standards are prepared using at least twopolybutadienes of known trans-content (e.g., high and low percenttrans-polybutadiene). These samples are used alone and blended togetherin such a way as to create a ladder of trans-polybutadiene content of atleast about 1.5% to 50% or to bracket the unknown amount, such that theresulting calibration curve contains at least about 13 equally spacedpoints.

[0084] Using a Fourier Transform Raman (“FT-Raman”) spectrometerequipped with a near-infrared laser, a Stokes Raman spectrum should beobtained from each standard using the following instrument parameters:sufficient laser power to obtain a good signal-to-noise ratio (“S/N”)without causing excessive heating or fluorescence (typically about 400to 800 mW is suitable); a resolution of 2 cm⁻¹; over a Raman shiftspectral range of about 400 to 4000 cm⁻¹; and co-adding at least 300scans.

[0085] A calibration curve may be constructed from the data generatedabove, using a chemometrics approach and software such as PLSplus/IQfrom Galactic Industries Corp. of Salem, N.H. An acceptable calibrationwas obtained with this software using a PLS-1 curve generated using anSNV (detrend) pathlength correction, a mean center data preparation, anda 5-point SG second derivative over the spectral range from about 1600to 1700 cm⁻¹. The correlation coefficient (R²) of the resultingcalibration curve must be a minimum of 0.95.

[0086] A Raman spectrum of the core material is obtained using thisinstrument at the point of interest in the sample (e.g., surface orcenter of the golf ball core). The sample must be free of foreignmatter, such as mold release, etc. Analyze the spectrum of the sampleusing the PLS calibration curve to determine trans-polybutadiene isomercontent of the sample.

[0087] A free-radical source, often alternatively referred to as afree-radical initiator, is required in the composition and method. Thefree-radical source is typically a peroxide, and preferably an organicperoxide. Suitable free-radical sources include di-t-amyl peroxide,di(2-t-butyl-peroxyisopropyl)benzene peroxide,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, dicumyl peroxide,di-t-butyl peroxide, 2,5-di-(t-butylperoxy)-2,5-dimethyl hexane,n-butyl-4,4-bis(t-butylperoxy)valerate, lauryl peroxide, benzoylperoxide, t-butyl hydroperoxide, and the like, and any mixture thereofThe peroxide is typically present in an amount greater than about 0.1parts per hundred of the total resilient polymer component, preferablyabout 0.1 to 15 parts per hundred of the resilient polymer component,and more preferably about 0.2 to 5 parts per hundred of the totalresilient polymer component. It should be understood by those ofordinary skill in the art that the presence of certain cis-to-transcatalysts according to the invention may require a larger amount offree-radical source, such as the amounts described herein, compared toconventional cross-linking reactions. The free radical source mayalternatively or additionally be one or more of an electron beam, UV orgamma radiation, x-rays, or any other high energy radiation sourcecapable of generating free radicals. It should be further understoodthat heat often facilitates initiation of the generation of freeradicals.

[0088] Crosslinkers are included to increase the hardness of thereaction product. Suitable crosslinkinig agents include one or moremetallic salts of unsaturated fatty acids or monocarboxylic acids, suchas zinc, calcium, or magnesium acrylate salts, and the like, andmixtures thereof. Preferred acrylates include zinc acrylate, zincdiacrylate, zinc methacrylate, and zinc dimethacrylate, and mixturesthereof. The crosslinking agent must be present in an amount sufficientto crosslink a portion of the chains of polymers in the resilientpolymer component. For example, the desired compression may be obtainedby adjusting the amount of crosslinking. This may be achieved, forexample, by altering the type and amount of crosslinking agent, a methodwell-known to those of ordinary skill in the art. The crosslinking agentis typically present in an amount greater than about 0.1 percent of theresilient polymer component, preferably from about 10 to 40 percent ofthe resilient polymer component, more preferably from about 10 to 30percent of the resilient polymer component. When an organosulfur isselected as the cis-to-trans catalyst, zinc diacrylate may be selectedas the crosslinking agent and is present in an amount of less than about25 phr.

[0089] Fillers added to one or more portions of the golf ball typicallyinclude processing aids or compounds to affect Theological and mixingproperties, the specific gravity (i.e., density-modifying fillers), themodulus, the tear strength, reinforcement, and the like. The fillers aregenerally inorganic, and suitable fillers include numerous metals ormetal oxides, such as zinc oxide and tin oxide, as well as bariumsulfate, zinc sulfate, calcium carbonate, barium carbonate, clay,tungsten, tungsten carbide, an array of silicas, and mixtures thereof.Fillers may also include various foaming agents or blowing agents whichmay be readily selected by one of ordinary skill in the art. Polymeric,ceramic, metal, and glass microspheres may be solid or hollow, andfilled or unfilled. Fillers are typically also added to one or moreportions of the golf ball to modify the density thereof to conform touniform golf ball standards. Fillers may also be used to modify theweight of the center or at least one additional layer for specialtyballs, e.g., a lower weight ball is preferred for a player having a lowswing speed.

[0090] The polymers, free-radical initiator, filler(s), and any othermaterials used in forming either the golf ball center or any portion ofthe core, in accordance with invention, may be combined to form amixture by any type of mixing known to one of ordinary skill in the art.Suitable types of mixing include single pass and multi-pass mixing, andthe like. The crosslinking agent, and any other optional additives usedto modify the characteristics of the golf ball center or additionallayer(s), may similarly be combined by any type of mixing. A single-passmixing process where ingredients are added sequentially is preferred, asthis type of mixing tends to increase efficiency and reduce costs forthe process. The preferred mixing cycle is single step wherein thepolymer, cis-trans catalyst, filler, zinc diacrylate, and peroxide areadded sequentially. Suitable mixing equipment is well known to those ofordinary skill in the art, and such equipment may include a Banburymixer, a two-roll mill, or a twin screw extruder. Conventional mixingspeeds for combining polymers are typically used, although the speedmust be high enough to impart substantially uniform dispersion of theconstituents. On the other hand, the speed should not be too high, ashigh mixing speeds tend to break down the polymers being mixed andparticularly may undesirably decrease the molecular weight of theresilient polymer component. The speed should thus be low enough toavoid high shear, which may result in loss of desirably high molecularweight portions of the polymer component. Also, too high a mixing speedmay undesirably result in creation of enough heat to initiate thecrosslinking before the preforms are shaped and assembled around a core.The mixing temperature depends upon the type of polymer components, andmore importantly, on the type of free-radical initiator. For example,when using di(2-t-butyl-peroxyisopropyl)benzene as the free-radicalinitiator, a mixing temperature of about 80° C. to 125° C., preferablyabout 88° C. to 110° C., and more preferably about 90° C. to 100° C., issuitable to safely mix the ingredients. Additionally, it is important tomaintain a mixing temperature below the peroxide decompositiontemperature. For example, if dicumyl peroxide is selected as theperoxide, the temperature should not exceed 200° F. Suitable mixingspeeds and temperatures are well-known to those of ordinary skill in theart, or may be readily determined without undue experimentation.

[0091] The mixture can be subjected to, e.g., a compression or injectionmolding process, to obtain solid spheres for the center or hemisphericalshells for forming an intermediate layer. The polymer mixture issubjected to a molding cycle in which heat and pressure are appliedwhile the mixture is confined within a mold. The cavity shape depends onthe portion of the golf ball being formed. The compression and heatliberates free radicals by decomposing one or more peroxides, which mayinitiate the cis-to-trans conversion and crosslinking simultaneously.The temperature and duration of the molding cycle are selected basedupon the type of peroxide and cis-trans catalyst selected. The moldingcycle may have a single step of molding the mixture at a singletemperature for a fixed time duration. An example of a single stepmolding cycle, for a mixture that contains dicumyl peroxide, would holdthe polymer mixture at 340° F. for a duration of 15 minutes. The moldingcycle may also include a two-step process, in which the polymer mixtureis held in the mold at an initial temperature for an initial duration oftime, followed by holding at a second, typically higher temperature fora second duration of time. An example of a two-step molding cycle wouldbe holding the mold at 290° F. for 40 minutes, then ramping the mold to340° F. where it is held for a duration of 20 minutes. In a preferredembodiment of the current Invention, a single-step cure cycle isemployed. Single-step processes are effective and efficient, reducingthe time and cost of a two-step process. The resilient polymercomponent, polybutadiene, cis-to-trans trans conversion catalyst,additional polymers, free-radical initiator, filler, and any othermaterials used in forming either the golf ball center or any portion ofthe core, in accordance with the invention, may be combined to form agolf ball by an injection molding process, which is also well-known toone of ordinary skill in the art. Although the curing time depends onthe various materials selected, a particularly suitable curing time isabout 5 to 18 minutes, preferably from about 8 to 15 minutes, and morepreferably from about 10 to 12 minutes. Those of ordinary skill in theart will be readily able to adjust the curing time upward or downwardbased on the particular materials used and the discussion herein.

[0092] The cured resilient polymer component, which contains a greateramount of trans-polybutadiene than the uncured resilient polymercomponent, is formed into an article having a first hardness at a pointin the interior and a surface having a second hardness such that thesecond hardness differs from the first hardness by greater than 10percent of the first hardness. Preferably, the article is a sphere andthe point is the midpoint of the article. In another embodiment, thesecond hardness differs from the first by greater than 20 percent of thefirst hardness. The cured article also has a first amount oftrans-polybutadiene at an interior location and a second amount oftrans-polybutadiene at a surface location, wherein the first amount isat least about 6 percent less than the second amount, preferably atleast about 10 percent less than the second amount, and more preferablyat least about 20 percent less than the second amount. The interiorlocation is preferably a midpoint and the article is preferably asphere. The compression of the core, or portion of the core, of golfballs prepared according to the invention is preferably below about 50,more preferably below about 25.

[0093] The cover provides the interface between the ball and a club.Properties that are desirable for the cover are good moldability, highabrasion resistance, high tear strength, high resilience, and good moldrelease, among others. The cover typically has a thickness to providesufficient strength, good performance characteristics and durability.The cover preferably has a thickness of less than about 0.1 inches, morepreferably, less than about 0.05 inches, and most preferably, betweenabout 0.02 and about 0.04 inches. The invention is particularly directedtowards a multilayer golf ball which comprises a core, an inner coverlayer, and an outer cover layer. In this embodiment, preferably, atleast one of the inner and outer cover layers has a thickness of lessthan about 0.05 inches, more preferably between about 0.02 and about0.04 inches. Most preferably, the thickness of either layer is about0.03 inches.

[0094] When the golf ball of the present invention includes anintermediate layer, such as an inner cover layer, this layer can includeany materials known to those of ordinary skill in the art, includingthermoplastic and thermosetting materials, but preferably theintermediate layer can include any suitable materials, such as ioniccopolymers of ethylene and an unsaturated monocarboxylic acid which areavailable under the trademark SURLYN of E. I. DuPont de Nemours & Co.,of Wilmington, Del., or IOTEK or ESCOR of Exxon. These are copolymers orterpolymers of ethylene and methacrylic acid or acrylic acid partiallyneutralized with salts of zinc, sodium, lithium, magnesium, potassium,calcium, manganese, nickel or the like, in which the salts are thereaction product of an olefin having from 2 to 8 carbon atoms and anunsaturated monocarboxylic acid having 3 to 8 carbon atoms. Thecarboxylic acid groups of the copolymer may be totally or partiallyneutralized and might include methacrylic, crotonic, maleic, fumaric oritaconic acid.

[0095] This golf ball can likewise include one or more homopolymeric orcopolymeric intermediate materials, such as:

[0096] (1) Vinyl resins, such as those formed by the polymerization ofvinyl chloride, or by the copolymerization of vinyl chloride with vinylacetate, acrylic esters or vinylidene chloride;

[0097] (2) Polyolefins, such as polyethylene, polypropylene,polybutylene and copolymers such as ethylene methylacrylate, ethyleneethylacrylate, ethylene vinyl acetate, ethylene methacrylic or ethyleneacrylic acid or propylene acrylic acid and copolymers and homopolymersproduced using a single-site catalyst or a metallocene catalyst;

[0098] (3) Polyurethanes, such as those prepared from polyols anddiisocyanates or polyisocyanates and those disclosed in U.S. Pat. No.5,334,673;

[0099] (4) Polyureas, such as those disclosed in U.S. Pat. No.5,484,870;

[0100] (5) Polyamides, such as poly(hexamethylene adipamide) and othersprepared from diamines and dibasic acids, as well as those from aminoacids such as poly(caprolactam), and blends of polyamides with SURLYN,polyethylene, ethylene copolymers, ethyl-propylene-non-conjugated dieneterpolymer, and the like;

[0101] (6) Acrylic resins and blends of these resins with poly vinylchloride, elastomers, and the like;

[0102] (7) Thermoplastics, such as urethanes; olefinic thermoplasticrubbers, such as blends of polyolefins withethylene-propylene-non-conjugated diene terpolymer; block copolymers ofstyrene and butadiene, isoprene or ethylene-butylene rubber; orcopoly(ether-amide), such as PEBAX, sold by ELF Atochem of Philadelphia,Pa.;

[0103] (8) Polyphenylene oxide resins or blends of polyphenylene oxidewith high impact polystyrene as sold under the trademark NORYL byGeneral Electric Company of Pittsfield, Mass.;

[0104] (9) Thermoplastic polyesters, such as polyethylene terephthalate,polybutylene terephthalate, polyethylene terephthalate/glycol modifiedand elastomers sold under the trademarks HYTREL by E. I. DuPont deNemours & Co. of Wilmington, Del., and LOMOD by General Electric Companyof Pittsfield, Mass.;

[0105] (10) Blends and alloys, including polycarbonate withacrylonitrile butadiene styrene, polybutylene terephthalate,polyethylene terephthalate, styrene maleic anhydride, polyethylene,elastomers, and the like, and polyvinyl chloride with acrylonitrilebutadiene styrene or ethylene vinyl acetate or other elastomers; and

[0106] (11) Blends of thermoplastic rubbers with polyethylene,propylene, polyacetal, nylon, polyesters, cellulose esters, and thelike.

[0107] Preferably, the optional intermediate layer includes polymers,such as ethylene, propylene, butene-1 or hexane-1 based homopolymers orcopolymers including functional monomers, such as acrylic andmethacrylic acid and fully or partially neutralized ionomer resins andtheir blends, methyl acrylate, methyl methacrylate homopolymers andcopolymers, imidized, amino group containing polymers, polycarbonate,reinforced polyamides, polyphenylene oxide, high impact polystyrene,polyether ketone, polysulfone, poly(phenylene sulfide),acrylonitrile-butadiene, acrylic-styrene-acrylonitrile, poly(ethyleneterephthalate), poly(butylene terephthalate), poly(ethylene vinylalcohol), poly(tetrafluoroethylene) and their copolymers includingfunctional comonomers, and blends thereof. Suitable cover compositionsalso include a polyether or polyester thermoplastic urethane, athermoset polyurethane, a low modulus ionomer, such as acid-containingethylene copolymer ionomers, including E/X/Y terpolymers where E isethylene, X is an acrylate or methacrylate-based softening comonomerpresent in about 0 to 50 weight percent and Y is acrylic or methacrylicacid present in about 5 to 35 weight percent. More preferably, in a lowspin rate embodiment designed for maximum distance, the acrylic ormethacrylic acid is present in about 15 to 35 weight percent, making theionomer a high modulus ionomer. In a high spin embodiment, the coverincludes an ionomer where an acid is present in about 10 to 15 weightpercent and includes a softening comonomer.

[0108] The cover preferably include a polyurethane compositioncomprising the reaction product of at least one polyisocyanate, polyol,and at least one curing agent.

[0109] Any polyisocyanate available to one of ordinary skill in the artis suitable for use according to the invention. Exemplarypolyisocyanates include, but are not limited to, 4,4′-diphenylmethanediisocyanate (“MDI”), polymeric MDI, carboduimide-modified liquid MDI,4,4′-dicyclohexylmethane diisocyanate (“H₁₂MDI”),p-phenylenediisocyanate (“PPDI”), toluene diisocyanate (“TDI”),3,3′-dimethyl-4,4′-biphenylene diisocyanate (“TODI”),isophoronediisocyanate (“IPDI”), hexamethylene diisocyanate (“HDI”),naphthalene diisocyanate (“NDI”); xylene diisocyanate (“XDI”);para-tetramethylxylene diisocyanate (“p-TMXDI”); meta-tetramethylxylenediisocyanate (“m-TMXDI”); ethylene diisocyanate;propylene-1,2-diisocyanate; tetramethylene-1,4-diisocyanate; cyclohexyldiisocyanate; 1,6-hexamethylene-diisocyanate (“HDI”);dodecane-1,12-diisocyanate; cyclobutane-1,3-diisocyanate;cyclohexane-1,3-diisocyanate; cyclohexane-1,4-diisocyanate;1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane; methylcyclohexylene diisocyanate; triisocyanate of HDI; triisocyanate of2,4,4-trimethyl-1,6-hexane diisocyanate (“TMDI”), tetracenediisocyanate, napthalene diisocyanate, anthracene diisocyanate, andmixtures thereof. Polyisocyanates are known to those of ordinary skillin the art as having more than one isocyanate group, e.g., di-, tri-,and tetra-isocyanate. Preferably, the polyisocyanate includes MDI, PPDI,TDI, or a mixture thereof, and more preferably, the polyisocyanateincludes MDI. It should be understood that, as used herein, the term“MDI” includes 4,4′-diphenylmethane diisocyanate, polymeric MDI,carboduimide-modified liquid MDI, and mixtures thereof and,additionally, that the diisocyanate employed may be “low free monomer,”understood by one of ordinary skill in the art to have lower levelsof“free” monomer isocyanate groups, typically less than about 0.1% freemonomer groups. Examples of “low free monomer” diisocyanates include,but are not limited to Low Free Monomer MDI, Low Free Monomer TDI, andLow Free Monomer PPDI.

[0110] The at least one polyisocyanate should have less than about 14%unreacted NCO groups. Preferably, the at least one polyisocyanate has nogreater than about 7.5% NCO, more preferably, between about 2.5% andabout 7.5%, and most preferably, between about 4% to about 6.5%.

[0111] Any polyol available to one of ordinary skill in the art issuitable for use according to the invention. Exemplary polyols include,but are not limited to, polyether polyols, hydroxy-terminatedpolybutadiene (including partially/fully hydrogenated derivatives),polyester polyols, polycaprolactone polyols, and polycarbonate polyols.In one preferred embodiment, the polyol includes polyether-polyol, morepreferably those polyols that have the generic structure:

[0112] where R₁ and R₂ are straight or branched hydrocarbon chains, eachcontaining from 1 to about 20 carbon atoms, and n ranges from 1 to about45. Examples include, but are not limited to, polytetramethylene etherglycol (“PTMEG”), polyethylene propylene glycol, polyoxypropyleneglycol, and mixtures thereof. The hydrocarbon chain can have saturatedor unsaturated bonds and substituted or unsubstituted aromatic andcyclic groups. Preferably, the polyol of the present invention includesPTMEG.

[0113] In another embodiment, polyester polyols are included in thepolyurethane material of the invention. Preferred polyester polyols havethe generic structure:

[0114] where R₁ and R₂ are straight or branched hydrocarbon chains, eachcontaining from 1 to about 20 carbon atoms, and n ranges from 1 to about25. Suitable polyester polyols include, but are not limited to,polyethylene adipate glycol, polybutylene adipate glycol, polyethylenepropylene adipate glycol, ortho-phthalate-1,6-hexanediol, and mixturesthereof. The hydrocarbon chain can have saturated or unsaturated bonds,or substituted or unsubstituted aromatic and cyclic groups.

[0115] In another embodiment, polycaprolactone polyols are included inthe materials of the invention. Preferably, any polycaprolactone polyolshave the generic structure:

[0116] where R₁ is a straight chain or branched hydrocarbon chaincontaining from 1 to about 20 carbon atoms, and n is the chain lengthand ranges from 1 to about 20. Suitable polycaprolactone polyolsinclude, but are not limited to, 1,6-hexanediol-initiatedpolycaprolactone, diethylene glycol initiated polycaprolactone,trimethylol propane initiated polycaprolactone, neopentyl glycolinitiated polycaprolactone, 1,4-butanediol-initiated polycaprolactone,and mixtures thereof. The hydrocarbon chain can have saturated orunsaturated bonds, or substituted or unsubstituted aromatic and cyclicgroups.

[0117] In yet another embodiment, the polycarbonate polyols are includedin the polyurethane material of the invention. Preferably, anypolycarbonate polyols have the generic structure:

[0118] where R₁ is predominantly bisphenol A units-(p-C₆H₄)—C(CH₃)₂-(p-C₆H₄)—or derivatives thereof, and n is the chainlength and ranges from 1 to about 20. Suitable polycarbonates include,but are not limited to, polyphthalate carbonate. The hydrocarbon chaincan have saturated or unsaturated bonds, or substituted or unsubstitutedaromatic and cyclic groups. In one embodiment, the molecular weight ofthe polyol is from about 200 to about 4000.

[0119] Polyamine curatives are also suitable for use in the polyurethanecomposition of the invention and have been found to improve cut, shear,and impact resistance of the resultant balls. Preferred polyaminecuratives include, but are not limited to,3,5-dimethylthio-2,4-toluenediamine and isomers thereof;3,5-diethyltoluene-2,4-diamine and isomers thereof, such as3,5-diethyltoluene-2,6-diamine;4,4′-bis-(sec-butylamino)-diphenylmethane;1,4-bis-(sec-butylamino)-benzene, 4,4′-methylene-bis-(2-chloroaniline);4,4′-methylene-bis-(3-chloro-2,6-diethylaniline);polytetramethyleneoxide-di-p-aminobenzoate; N,N′-dialkyldiamino diphenylmethane; p,p′-methylene dianiline (“MDA”); m-phenylenediamine (“MPDA”);4,4′-methylene-bis-(2-chloroaniline) (“MOCA”);4,4′-methylene-bis-(2,6-diethylaniline);4,4′-diamino-3,3′-diethyl-5,5′-dimethyl diphenylmethane;2,2′,3,3′-tetrachloro diamino diphenylmethane;4,4′-methylene-bis-(3-chloro-2,6-diethylaniline); trimethylene glycoldi-p-aminobenzoate; and mixtures thereof. Preferably, the curing agentof the present invention includes 3,5-dimethylthio-2,4-toluenediamineand isomers thereof, such as ETHACURE 300, commercially available fromAlbermarle Corporation of Baton Rouge, La. Suitable polyamine curatives,which include both primary and secondary amines, preferably havemolecular weights ranging from about 64 to about 2000.

[0120] Other suitable polyamine curatives include those having thegeneral formula:

[0121] where n and m each separately have values of 0, 1, 2, or 3, andwhere Y is 1,2-cyclohexyl, 1,3-cyclohexyl, 1,4-cyclohexyl,ortho-phenylene, meta-phenylene, or para-phenylene, or a combinationthereof. Preferably, n and m, each separately, have values of 0, 1, or2, and preferably, 1 or 2.

[0122] At least one of a diol, triol, tetraol, or hydroxy-terminatedcuratives may be added to the aforementioned polyurethane composition.Suitable diol, triol, and tetraol groups include ethylene glycol;diethylene glycol; polyethylene glycol; propylene glycol; polypropyleneglycol; lower molecular weight polytetramethylene ether glycol;1,3-bis(2-hydroxyethoxy)benzene;1,3-bis-[2-(2-hydroxyethoxy)ethoxy]benzene;1,3-bis-{2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}benzene; 1,4-butanediol;1,5-pentanediol; 1,6-hexanediol; resorcinol-di-(β-hydroxyethyl)ether;hydroquinone-di-(β-hydroxyethyl)ether; and mixtures thereof. Preferredhydroxy-terminated curatives include ethylene glycol; diethylene glycol;1,4-butanediol; 1,5-pentanediol; 1,6-hexanediol, trimethylol propane,and mixtures thereof.

[0123] Preferably, the hydroxy-terminated curatives have molecularweights ranging from about 48 to 2000. It should be understood thatmolecular weight, as used herein, is the absolute weight averagemolecular weight and would be understood as such by one of ordinaryskill in the art. Other suitable hydroxy-terminated curatives have thefollowing general chemical structure:

[0124] where n and m each separately have values of 0, 1, 2, or 3, andwhere X is ortho-phenylene, meta-phenylene, para-phenylene,1,2-cyclohexyl, 1,3-cyclohexyl, or 1,4-cyclohexyl, or mixtures thereof.Preferably, n and m each separately have values of 0, 1, or 2, and morepreferably, 1 or 2.

[0125] Both the hydroxy-terminated and amine curatives can include oneor more saturated, unsaturated, aromatic, and cyclic groups.Additionally, the hydroxy-terminated and amine curatives can include oneor more halogen groups. The polyurethane composition can be formed witha blend or mixture of curing agents. If desired, however, thepolyurethane composition may be formed with a single curing agent.

[0126] Any method known to one of ordinary skill in the art may be usedto combine the polyisocyanate, polyol, and curing agent of the presentinvention. One commonly employed method, known in the art as a one-shotmethod, involves concurrent mixing of the polyisocyanate, polyol, andcuring agent. This method results in a mixture that is inhomogenous(more random) and affords the manufacturer less control over themolecular structure of the resultant composition. A preferred method ofmixing is known as a prepolymer method. In this method, thepolyisocyanate and the polyol are mixed separately prior to addition ofthe curing agent. This method affords a more homogeneous mixtureresulting in a more consistent polymer composition.

[0127] An optional filler component may be chosen to impart additionaldensity to blends of the previously described components. The selectionof such filler(s) is dependent upon the type of golf ball desired (i.e.,one-piece, two-piece multi-component, or wound). Examples of usefulfillers include zinc oxide, barium sulfate, calcium oxide, calciumcarbonate and silica, as well as the other well known correspondingsalts and oxides thereof. Additives, such as nanoparticles, glassspheres, and various metals, such as titanium and tungsten, can be addedto the polyurethane compositions of the present invention, in amounts asneeded, for their well-known purposes. Additional components which canbe added to the polyurethane composition include UV stabilizers andother dyes, as well as optical brighteners and fluorescent pigments anddyes. Such additional ingredients may be added in any amounts that willachieve their desired purpose.

[0128] Due to the very thin nature, it has been found by the presentinvention that the use of a castable, reactive material, which isapplied in a fluid form, makes it possible to obtain very thin outercover layers on golf balls. Specifically, it has been found thatcastable, reactive liquids, which react to form a urethane elastomermaterial, provide desirable very thin outer cover layers.

[0129] The castable, reactive liquid employed to form the urethaneelastomer material can be applied over the inner core using a variety ofapplication techniques such as spraying, dipping, spin coating, or flowcoating methods which are well known in the art. An example of asuitable coating technique is that which is disclosed in U.S. Pat. No.5,733,428, filed May 2, 1995 entitled “Method And Apparatus For FormingPolyurethane Cover On A Golf Ball”, the disclosure of which is herebyincorporated by reference in its entirety in the present application.

[0130] The cover is preferably formed around the coated core by mixingand introducing the material in the mold halves. It is important thatthe viscosity be measured over time, so that the subsequent steps offilling each mold half, introducing the core into one half and closingthe mold can be properly timed for accomplishing centering of the corecover halves fusion and achieving overall uniformity. Suitable viscosityrange of the curing urethane mix for introducing cores into the moldhalves is determined to be approximately between about 2,000 cP andabout 30,000 cP, with the preferred range of about 8,000 cP to about15,000 cP.

[0131] To start the cover formation, mixing of the prepolymer andcurative is accomplished in motorized mixer including mixing head byfeeding through lines metered amounts of curative and prepolymer. Toppreheated mold halves are filled and placed in fixture units using pinsmoving into holes in each mold. After the reacting materials haveresided in top mold halves for about 50 to about 80 seconds, a core islowered at a controlled speed into the gelling reacting mixture. At alater time, a bottom mold half or a series of bottom mold halves havesimilar mixture amounts introduced into the cavity.

[0132] A ball cup holds the ball core through reduced pressure (orpartial vacuum) in hose. Upon location of the coated core in the halvesof the mold after gelling for about 50 to about 80 seconds, the vacuumis released allowing core to be released. The mold halves, with core andsolidified cover half thereon, are removed from the centering fixtureunit, inverted and mated with other mold halves which, at an appropriatetime earlier, have had a selected quantity of reacting polyurethaneprepolymer and curing agent introduced therein to commence gelling.

[0133] Similarly, U.S. Pat. No. 5,006,297 to Brown et al. and U.S. Pat.No. 5,334,673 to Wu both also disclose suitable molding techniques whichmay be utilized to apply the castable reactive liquids employed in thepresent invention. The disclosures of these patents are herebyincorporated by reference in their entirety. However, the method of theinvention is not limited to the use of these techniques.

[0134] Depending on the desired properties, balls prepared according tothe invention can exhibit substantially the same or higher resilience,or coefficient of restitution (“COR”), with a decrease in compression ormodulus, compared to balls of conventional construction. Additionally,balls prepared according to the invention can also exhibit substantiallyhigher resilience, or COR without an increase in compression, comparedto balls of conventional construction. Another measure of thisresilience is the “loss tangent,” or tan δ, which is obtained whenmeasuring the dynamic stiffness of an object. Loss tangent andterminology relating to such dynamic properties is typically describedaccording to ASTM D4092-90. Thus, a lower loss tangent indicates ahigher resiliency, thereby indicating a higher rebound capacity. Lowloss tangent indicates that most of the energy imparted to a golf ballfrom the club is converted to dynamic energy, i.e., launch velocity andresulting longer distance. The rigidity or compressive stiffness of agolf ball may be measured, for example, by the dynamic stiffness. Ahigher dynamic stiffness indicates a higher compressive stiffness. Toproduce golf balls having a desirable compressive stiffness, the dynamicstiffness of the crosslinked reaction product material should be lessthan about 50,000 N/m at −50° C. Preferably, the dynamic stiffnessshould be between about 10,000 and 40,000 N/m at −50° C., morepreferably, the dynamic stiffness should be between about 20,000 and30,000 N/m at −50° C.

[0135] The dynamic stiffness is similar in some ways to dynamic modulus.Dynamic stiffness is dependent on probe geometry as described herein,whereas dynamic modulus is a unique material property, independent ofgeometry. The dynamic stiffness measurement has the unique attribute ofenabling quantitative measurement of dynamic modulus and exactmeasurement of loss tangent at discrete points within a sample article.In the case of this invention, the article is a golf ball core. Thepolybutadiene reaction product preferably has a loss tangent below about0.1 at −50° C., and more preferably below about 0.07 at −50° C.

[0136] The resultant golf balls typically have a coefficient ofrestitution of greater than about 0.7, preferably greater than about0.75, and more preferably greater than about 0.78. The golf balls alsotypically have an Atti compression (which has been referred to as PGAcompression in the past) of at least about 40, preferably from about 50to 120, and more preferably from about 60 to 100. The golf ballpolybutadiene material of the present invention typically has a flexuralmodulus of from about 500 psi to 300,000 psi, preferably from about 2000to 200,000 psi. The golf ball polybutadiene material typically has ahardness of at least about 15 Shore A, preferably between about 30 ShoreA and 80 Shore D, more preferably between about 50 Shore A and 60 ShoreD. The specific gravity is typically greater than about 0.7, preferablygreater than about 1, for the golf ball polybutadiene material.

[0137] The center composition should comprise at least one rubbermaterial having a resilience index of at least about 40. Preferably theresilience index is at least about 50. A comparison of a number ofpolybutadiene polymers are listed in Table 1 below. Polymers thatproduce resilient golf balls and, therefore, are suitable for thepresent invention, include but are not limited to CB23, CB22, BR60, and1207G. To clarify the method of computation for resilience index, theresilience index for CB23, for example, is computed as follows:

Resilience Index for CB23=100,000·[(0.954)−(0.407)]/990

Resilience Index for CB23=55

[0138] TABLE 1 Resilience Index of example polybutadiene polymers Tan δat Resilience Index at Rubber 10 cpm 1000 cpm 100° C. CB23 0.954 0.40755 CB22 0.895 0.358 54 BR-60 0.749 0.350 40 BR-40 0.841 0.446 40 Taktene8855 0.720 0.414 31 CARIFLEX BR1220 0.487 0.439 5 BUDENE 1207G 0.8250.388 44

[0139] The molding process and composition of golf ball portionstypically results in a gradient of material properties. Methods employedin the prior art generally exploit hardness to quantify these gradients.Hardness is a qualitative measure of static modulus and does notrepresent the modulus of the material at the deformation ratesassociated with golf ball use, i.e., impact by a club. As is well knownto one skilled in the art of polymer science, the time-temperaturesuperposition principle may be used to emulate alternative deformationrates. For golf ball portions including polybutadiene, a 1-Hzoscillation at temperatures between 0° C. and −50° C. are believed to bequalitatively equivalent to golf ball impact rates. Therefore,measurement of loss tangent and dynamic stiffness at 0° C. to −50° C.may be used to accurately anticipate golf ball performance, preferablyat temperatures between about −20° C. and −50° C.

[0140] Additionally, the unvulcanized rubber, such as polybutadiene, ingolf balls prepared according to the invention typically has a Mooneyviscosity of between about 40 and about 80, more preferably, betweenabout 45 and about 60, and most preferably, between about 45 and about55. Mooney viscosity is typically measured according to ASTM D-1646.

[0141] When golf balls are prepared according to the invention, theytypically will have dimple coverage greater than about 60 percent,preferably greater than about 65 percent, and more preferably greaterthan about 75 percent. The flexural modulus of the cover on the golfballs, as measured by ASTM method D6272-98, Procedure B, is typicallygreater than about 500 psi, and is preferably from about 500 psi to150,000 psi. As discussed herein, the outer cover layer is preferablyformed from a relatively soft polyurethane material. In particular, thematerial of the outer cover layer should have a material hardness, asmeasured by ASTM-2240, between about 30 and about 60 Shore D, preferablyfrom about 35 to about 55 Shore D. The inner cover layer, if present,preferably has a material hardness from about 50 to about 75 Shore D,preferably from about 60 to about 65 Shore D.

EXAMPLES

[0142] A variety of cores were prepared according to the presentinvention, as well as some cores prepared using conventional materials.All cores in Table 2 were prepared to a diameter of 1.58 inches. Therecipes for each core, and values measured for compression and COR arepresented in Table 2 below: TABLE 2 Golf Ball Core Properties fromVarious Rubber Formulations Mooney viscosity Ingredients @ 100° C. 1 2 34 5 CB23 51 100 CB22 63 100 BR-60 60 100 Taktene 8855 48 100 CARIFLEXBR1220 43 100 zinc diacrylate 28 28 28 28 28 peroxide 0.53 0.53 0.530.53 0.53 zinc oxide 4.3 4.3 4.3 4.3 4.3 tungsten 11.0 11.0 11.0 11.011.0 Core Properties compression 77 75 77 76 71 COR @ 125 ft/s 0.8150.811 0.810 0.807 0.802

[0143] A variety of metal sulfide cis-to-trans catalysts thatsuccessfully converted a portion of the cis-polybutadiene isomer to thetrans-isomer are presented in Table 3. CARIFLEX BR1220 polybutadiene(100 phr) was reacted with zinc oxide (5 phr), dicumyl peroxide (3 phr,the free radical initiator), and zinc diacrylate (25 phr), to form thereaction product as described in the present invention.

[0144] Trans-isomer conversion percentages range from below 8 percent toabove 17 percent for the various catalysts that are present in amountsranging from below 1.7 phr to above 3.7 phr. The table clearlydemonstrates the effectiveness of numerous different cis-to-transcatalysts, at varying concentrations, for increasing thetrans-polybutadiene content.

Example 1

[0145] A Core Prepared from According to the Invention Employing anOrganosulfur Cis-to-Trans Catalyst.

[0146] A core according to the present invention was created employingan organosulfur compound as the cis-to-trans conversion catalyst. Theresultant core properties clearly demonstrate the advantages of a golfball core made according to the current invention as compared to examplecores constructed with conventional technology. The components andphysical characteristics are presented in Table 4.

[0147] The compressive load of cores prepared according to the inventionis approximately half of the compressive load of cores constructed inaccordance with U.S. Pat. Nos. 5,697,856, 5,252,652, and 4,692,497,while at the same time retaining roughly the same, and in some caseshigher, COR (resilience). The core made according to the currentinvention has a lower compressive load (soft), yet is resilient (fast).The compressive load is greater than that of a core constructed inaccordance with U.S. Pat. No. 3,239,228, but has a significantly higherCOR. The core of U.S. Pat. No. 3,239,228 is very soft and very slow(very low COR).

[0148] The percent change in dynamic stiffness from 0° C. to −50° C. wasalso measured at both the edge and center of the cores. The dynamicstiffness at both the edge and the center of the core of the currentinvention varied only slightly, less than 20 percent, over thetemperature range investigated. The core made according to U.S. Pat. No.3,239,228 varied over 230 percent, whereas the cores made according toother conventional technology, had a dynamic stiffness that varied bygreater than 130 percent, and typically by as much as 150 percent, overthe same temperature range.

[0149] The percent of trans-conversion was also measured at both thecenter and edge of the core prepared according to the current invention,and for cores prepared as disclosed in the same four patents mentionedabove, allowing a trans-gradient to be calculated. The core according tothe current invention had a trans-gradient of about 32 percent from edgeto center. For the core prepared according to the current invention, thepre- and post-cure trans-percentages was also measured to determine theeffectiveness of that process. The percentage of polybutadiene convertedto the trans-isomer ranged from almost 40 percent at the center togreater than 55 percent at the edge. Two of the cores prepared accordingto conventional technology, U.S. Pat. Nos. 3,239,228 and 4,692,497, hada zero trans-gradient. A third core, prepared according to U.S. Pat. No.5,697,856, had only a slight trans-gradient, less than 18 percent fromedge to center. A fourth core, prepared according to U.S. Pat. No.5,252,652, had a very large gradient, almost 65 percent from edge tocenter. TABLE 3 Metal Sulfide Conversion Examples CARIFLEX BR1220 100100 100 100 100 100 100 100 100 100 100 100 100 Zinc oxide 5 5 5 5 5 5 55 5 5 5 5 5 Dicumyl peroxide 3 3 3 3 3 3 3 3 3 3 3 3 3 Zinc Diacrylate25 25 25 25 25 25 25 25 25 25 25 25 25 Cis-to-Trans “Catalyst” FeS 2.87MnS 2.65 TiS₂ 1.70 CaS 2.20 CoS 2.77 MoS₂ 2.43 WS₂ 3.77 Cu₂S 4.65 SeS₂2.19 Y₂ S₃ 2.76 ZnS 2.97 Sb₂ S₃ 3.45 Bi₂ S₃ 5.22 % Trans BR isomer 1.51.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Precure % Trans BRisomer 10.5 16.1 17.0 8.3 10.3 10.1 9.2 5.8 5.2 10.2 10.1 10.7 10.5Postcure

[0150] TABLE 4 Invention Examples of Conventional Golf Balls Examples US#5816944 US#4971329 Chemical Constituents #1 #2 #3 US#3239228 US#5697856US#5252652 US#4692497 Polybutadiene (Shell, CARIFLEX BR1220) 100 100 100N/A N/A N/A Polybutadiene (Firestone, 35 NF) 100 N/A N/A N/A DMDS 2.1N/A N/A N/A Carbon Black (RA) 15 N/A N/A N/A Wood Flour 24 N/A N/A N/ASulfur 24 N/A N/A N/A Stearic Acid 1.5 N/A N/A N/A Reogen 15 N/A N/A N/AVanox MBPC 2 N/A N/A N/A Triethanolamine 4 N/A N/A N/A Zinc oxide 5 5 55 N/A N/A N/A Dicumyl peroxide 3 1 9 2 N/A N/A N/A Zinc Diacrylate 25 2525 N/A N/A N/A Cis-Trans “Catalyst” N/A N/A N/A MnS 0.82 N/A N/A N/ADitolyldisulfide 2.5 1.5 N/A N/A N/A Cu₂S 1 N/A N/A N/A Resultant CoreProperties Load(lbs) @ 10.8% Deflection 1.580″ core 165.5 191.4 191.861.1 325 390 480 Coefficient of Restitution @ 125 ft/s 0.783 0.777 0.7850.599 0.779 0.805 0.775 Hardness Shore C Surface 61 76 62 35 75 80 80 5Center 52 52 59 30 70 61 66 5 Dynamic Stiffness @ 0° C. (N/m) Edge*25338 27676 28493 8312 62757 83032 72235 Center 20783 17390 27579 836161071 28264 50612 Dynamic Stiffness @ −50° C. (N/m) Edge* 30265 3452334455 19394 92763 109053 108242 Center 23022 20603 32195 18617 8967728808 83183 Dynamic Stiffness Ratio at −50° C./0° C. Edge* 119% 125%121% 233% 148% 131% 150% Center 111% 118% 117% 223% 147% 110% 164% LossTangent ° C. Edge* 0 024 0 027 0 024 0 074 0 039 0 037 0.045 Center0.025 0 023 0 023 0 073 0 033 0 025 0.043 Loss Tangent −50° C. Edge*0.098 0 084 0.097 0 183 0.142 0 119 0.099 Center 0 067 0 071 0 085 0 1800 129 0 059 0.095 % Trans BR isomer Precure 1.5 1.5 1.5 50 N/A N/A N/A %Trans BR isomer Postcure Surface 55.8 8.4 45.5 50 30.2 24.6 1.5 Center37.8 4.6 25.5 50 24.7 8.5 1.5 % Trans Variation (Surf. - Center)/ Surf.32% 45% 44% 0% 18% 65% 0%

Example 2

[0151] A Core Prepared from According to the Invention, Employing anInorganic Sulfide Cis-to-trans Catalyst.

[0152] A core according to the present invention was created employingan inorganic sulfide compound as the cis-to-trans conversion catalyst.The resultant core properties clearly demonstrate the advantages of agolf ball core made according to the current invention as compared toexample cores constructed with conventional technology. The componentsand physical characteristics are presented in Table 4.

[0153] The compressive load is approximately half of the compressiveload of three cores constructed in accordance with U.S. Pat. Nos.5,697,856, 5,252,652, and 4,692,497, while at the same time retainingroughly the same, and in some cases, a higher COR (resilience). The coremade according to the current invention is soft, yet resilient (fast).The compressive load is greater than a core constructed in accordancewith U.S. Pat. No. 3,239,228, but has a significantly higher COR. Thecore of U.S. Pat. No. 3,239,228 is very soft and very slow (low COR).

[0154] The percent change in dynamic stiffness from 0° C. to −50° C. wasalso measured at both the edge and center of the cores. The dynamicstiffness at both the edge and the center of the core of the currentinvention varied only slightly, less than 125 percent, over thetemperature range investigated. The core made according to U.S. Pat. No.3,239,228 varied over 230 percent, whereas the cores made according toother conventional technology, had a dynamic stiffness that varied bygreater than 130 percent, and typically by as much as 150 percent, overthe same temperature range.

[0155] The percent of trans-conversion was also measured at both thecenter and edge of the core prepared according to the current invention,and for cores prepared according to the same four patents mentionedabove, allowing a trans-gradient to be calculated. The core according tothe current invention had a trans-gradient of about 45 percent from edgeto center. Two of the cores prepared in accordance with U.S. Pat. Nos.3,239,228 and 4,692,497 had a zero trans-gradient. A third core,prepared in accordance with U.S. Pat. No. 5,697,856, had only a slighttrans-gradient, less than 18 percent from edge to center. A fourth core,prepared in accordance with U.S. Pat. No. 5,252,652, had a very largegradient, almost 65 percent, from edge to center.

Example 3

[0156] A Core Prepared from According to the Invention. Employing aBlend of Organosulfur and Inorganic Sulfide Cis-to-trans Catalyst.

[0157] A core according to the present invention was created employing ablend of organosulfur and inorganic sulfide compounds as thecis-to-trans conversion catalyst. The resultant core properties clearlydemonstrate the advantages of a golf ball core made according to thecurrent invention as compared to example cores constructed withconventional technology. The components and physical characteristics arepresented in Table 4.

[0158] The compressive load is approximately half of the compressiveload of three cores constructed in accordance with U.S. Pat. Nos.5,697,856, 5,252,652, and 4,692,497, while at the same time retainingroughly the same, and in some cases a higher COR (resilience). The coremade according to the current invention is soft, yet resilient (fast).The compressive load of the invention is greater than a fourth coreconstructed in accordance with U.S. Pat. No. 3,239,228, but has asignificantly higher COR. The core constructed in accordance with U.S.Pat. No. 3,239,228 is very soft and very slow (low COR).

[0159] The percent change in dynamic stiffness from 0° C. to −50° C. wasalso measured at both the edge and center of the cores. The dynamicstiffness at both the edge and the center of the core of the currentinvention varied only slightly, less than 121 percent, over thetemperature range investigated. The core made in accordance with U.S.Pat. No. 3,239,228 varied over 230 percent, whereas the cores madeaccording to other conventional technology had a dynamic stiffness thatvaried by greater than 130 percent, and typically by as much as 150percent, over the same temperature range.

[0160] The percent of trans-conversion was also measured at both thecenter and edge of the core prepared according to the current invention,and for cores prepared to the same four patents mentioned above,allowing a trans-gradient to be calculated. The core according to thecurrent invention had a trans-gradient that about 44 percent from edgeto center. For the core prepared according to the current invention, thepre- and post-cure trans-percentages was also measured to determine theeffectiveness of that process. The percentage of polybutadiene convertedto the trans-isomer ranged from almost 26 percent at the center togreater than 45 percent at the edge. Two of the cores prepared inaccordance with U.S. Pat. Nos. 3,239,228 and 4,692,497 had a zerotrans-gradient. A third core prepared in accordance with U.S. Pat. No.5,697,856 had only a slight trans-gradient, less than 18 percent fromedge to center. A fourth core, prepared in accordance with U.S. Pat. No.5,252,652 had a very large gradient, almost 65 percent from edge tocenter.

Example 4

[0161] Comparison of a Conventional Dual Core Ball to Dual Core BallPrepared According to the Invention.

[0162] A dual core golf ball according to the present invention wascreated having a solid center, an intermediate layer surrounding thesolid center, and a multilayer cover disposed concentrically around theintermediate layer. The components and physical characteristics arepresented below in Table 5. TABLE 5 Center Composition Example 4: DualCore CARIFLEX BR1220 100 zinc diacrylate 20 dicumyl peroxide 2.5 zincoxide 39 DTDS 0.75 Center Properties % trans Precure 1.5 % transPostcure 40 load in lbs required (10.8% deflection) 109 MantleComposition CB23 80 zinc diacrylate 38 VAROX 231 XL 0.42 DBDB-60 0.15zinc oxide 6 polyisoprene 20 Inner Cover Composition and Properties NaSURLYN 50 Li SURLYN 50 Shore D hardness 68 thickness 0.03 in Outer CoverComposition and Properties MDI polyurethane thickness 0.03 in

[0163] A solid center was constructed for the ball of the presentinvention. The center was created from CARIFLEX BR-1220 polybutadiene asthe starting material, the only difference being replacing the VAROX802-40KE-HP peroxide (conventional technology) with a DTDS cis-to-transcatalyst of the current invention and dicumyl peroxide. Thissubstitution allows a portion of the polybutadiene material to beconverted to the trails-configuration during the molding process. Theresulting solid center had an outside diameter of approximately 1.15inches. The polybutadiene reaction product prepared thereby had atrans-isomer content of 40 percent compared to the 1.5 percenttrans-isomer of conventional balls. An intermediate layer, havingoutside diameter of approximately 1.56 inches, was constructed aroundthe solid center to form a core. The outer layer is made of CB23 havinga molecular weight of about 360,000 and a Mooney viscosity of about 51.

Examples 5-8

[0164] Comparison of Conventional Golf Balls with those PreparedAccording to the Invention.

[0165] A polybutadiene reaction product was prepared for twoconventional prior art compositions (Examples 5-6) as well as oneprepared according to the invention (Examples 7-8). The recipes for eachcomposition can be seen in Table 6 below. TABLE 6 Example 5 Example 6Example 7 Example 8 Reaction Product (phr) (phr) (phr) (phr) CARIFLEXBR1220 100 100 100  100  zinc oxide 26.6 2.67   26.6   26.6 bariumsulfate — 31 — — zinc diacrylate 20 22.3 20 20 dicumyl peroxide 2 —  2 2 VAROX 802 40KE-HP^(a) — 0.89 — — polymeric sulfur 0 0    0.25  0elemental sulfur 0 0  0    0.25 pre-cure trans- 1.5% 1.5%      1.5%     1.5% polybutadiene content Golf Ball Core post-cure trans- 1.5%1.5%  12%  12% polybutadiene content in reaction product AttiCompression 53 23 26 21 COR n/a^(b) 0.72    0.77    0.76

[0166] These constituents were mixed and molded, thereby converting apercentage of cis- to a trans-conformation, in a solid sphere sized likethe core of a golf ball. Examples 7-8 illustrate the significantconversion of cis-polybutadienie to trans-polybutadiene when a sulfurcis-to-trans catalyst is present according to the invention compared tothe lack of conversion in Examples 5-6 when no sulfur catalyst ispresent. Moreover, Examples 7-8 illustrate the improved coefficient ofrestitution with no significant change in compression that can beachieved with golf balls including the reaction product according to theinvention.

[0167] The invention described and claimed herein is not to be limitedin scope by the specific embodiments herein disclosed, since theseembodiments are intended as illustrations of several aspects of theinvention. Any equivalent embodiments are intended to be within thescope of this invention. Indeed, various modifications of the inventionin addition to those shown and described herein will become apparent tothose skilled in the art from the foregoing description. Suchmodifications are also intended to fall within the scope of the appendedclaims.

What is claimed is:
 1. A golf ball comprising: a center comprising apolybutadiene having a molecular weight of greater than about 200,000and a resilience index of at least about 40; and a cover layercomprising a polyurethane composition formed from a prepolymer having nogreater than 7.5 percent by weight unreacted isocyanate groups.
 2. Thegolf ball of claim 1, wherein the resilience index is greater than about50.
 3. The golf ball of claim 1, wherein the polyurethane compositioncomprises at least one isocyanate, at least one polyol, and at least onecuring agent.
 4. The golf ball of claim 3, wherein the isocyanatecomprises 4,4′-diphenylmethane diisocyanate, polymeric4,4′-diphenylmethane diisocyanate, carbodiimide-modified liquid4,4′-diphenylmethane diisocyanate, 4,4′-dicyclohexylmethanediisocyanate, p-phenylene diisocyanate, toluene diisocyanate,isophoronediisocyanate, p-methylxylene diisocyanate, m-methylxylenediisocyanate, o-methylxylene diisocyanate, or a mixture thereof.
 5. Thegolf ball of claim 3, wherein the at least one polyol comprises apolyether polyol, hydroxy-terminated polybutadiene, polyester polyol,polycaprolactone polyol, polycarbonate polyol, or mixtures thereof. 6.The golf ball of claim 3, wherein the curing agent comprises a polyaminecuring agent, a polyol curing agent, or a mixture thereof.
 7. The golfball of claim 6, wherein the curing agent is a polyamine curing agent.8. The golf ball of claim 7, wherein the polyamine curing agentcomprises 3,5-dimethylthio-2,4-toluenediamine, or an isomer thereof;3,5-diethyltoluene-2,4-diamine, or an isomer thereof;4,4′-bis-(sec-butylamino)-diphenylmethane;1,4-bis-(sec-butylamino)-benzene,4,4′-methylene-bis-(2-chloroaniline);4,4′-methylene-bis-(3-chloro-2,6-diethylaniline); trimethyleneglycol-di-p-aminobenzoate; polytetramethyleneoxide-di-p-aminobenzoate;N,N′-dialkyldiamino diphenyl methane; p,p′-methylene dianiline;phenylenediamine; 4,4′-methylene-bis-(2-chloroaniline);4,4′-methylene-bis-(2,6-diethylaniline);4,4′-diamino-3,3′-diethyl-5,5′-dimethyl diphenylmethane;2,2′,3,3′-tetrachloro diamino diphenylmethane;4,4′-methylene-bis-(3-chloro-2,6-diethylaniline); or mixtures thereof.9. The golf ball of claim 6, wherein the curing agent is a polyol curingagent.
 10. The golf ball of claim 9, wherein the polyol curing agentcomprises ethylene glycol; diethylene glycol; polyethylene glycol;propylene glycol; polypropylene glycol; lower molecular weightpolytetramethylene ether glycol; 1,3-bis(2-hydroxyethoxy) benzene;1,3-bis-[2-(2-hydroxyethoxy)ethoxy]benzene;1,3-bis-{2-[2-(2-hydroxyethoxy) ethoxy]ethoxy}benzene; 1,4-butanediol;1,5-pentanediol; 1,6-hexanediol; resorcinol-di-(β-hydroxyethyl)ether;hydroquinone-di-(β-hydroxyethyl)ether; trimethylol propane, or mixturesthereof.
 11. The golf ball of claim 1, wherein the prepolymer has fromabout 2.5 percent up to 7.5 percent by weight unreacted isocyanategroups.
 12. The golf ball of claim 1, wherein the cover layer has athickness of less than about 0.05 inches.
 13. The golf ball of claim 1,wherein the center has a Mooney viscosity from about 40 to about
 80. 14.The golf ball of claim 13, wherein the Mooney viscosity from about 45 toabout
 60. 15. The golf ball of claim 1, wherein the polybutadiene has avinyl-isomer content of less than about 2 percent by weight.
 16. Thegolf ball of claim 1, wherein the polybutadiene has a cis-isomer contentof at least about 95 percent by weight.
 17. The golf ball of claim 1,wherein the center has an outer diameter of at least about 1.55 inches.18. The golf ball of claim 1, wherein the center further comprises amaterial formed from a conversion reaction of polybutadiene having afirst amount of trans-isomer, a free radical source, and at least onecis-to-trans catalyst.
 19. The golf ball of claim 18, wherein thereaction occurs at a temperature sufficient to form a polybutadienereaction product having a second amount of trans-isomer greater than thefirst amount of trans-isomer.
 20. The golf ball of claim 18, wherein thecis-to-trans catalyst further comprises at least one of an organosulfurcompound, an inorganic sulfur compound, an aromatic organometalliccompound, a metal-organosulfur compound, tellurium, selenium, elementalsulfur, a polymeric sulfur, or an aromatic organic compound.
 21. Thegolf ball of claim 20, wherein the organosulfur component comprises atleast one of 4,4′-diphenyl disulfide, 4,4′-ditolyl disulfide, or2,2′-benzamido diphenyl disulfide.
 22. The golf ball of claim 18,wherein the cis-to-trans catalyst is present in an amount from about 0.1to 10 parts per hundred of polybutadiene.
 23. The golf ball of claim 1,further comprising an intermediate layer between the center and thecover layer, wherein the intermediate layer comprises a material formedfrom a conversion reaction of polybutadiene having a first amount oftrans-polybutadiene, a free radical source, and a cis-to-trans catalystcomprising at least one organosulfur component, wherein the intermediatelayer has an outer diameter of at least about 1.58 inches, and whereinthe center has an outer diameter of less than about 1.55 inches.
 24. Thegolf ball of claim 1, wherein the cover comprises an inner cover layerand an outer cover layer, the inner cover layer disposed between thecenter and the outer cover layer.
 25. The golf ball of claim 24, whereinat least one of the inner and outer cover layer has a thickness of lessthan about 0.05 inches.
 26. The golf ball of claim 24, wherein the innercover layer comprises an ionomer resin, a polyurethane, apolyetherester, a polyetheramide, a polyester, a dynamically vulcanizedelastomer, a functionalized styrenebutadiene elastomer, a metallocenepolymer nylon, acrylonitrile butadiene-styrene copolymer, or blendsthereof.
 27. The golf ball of claim 24, wherein the inner cover has anouter diameter of at least about 1.55 inches.
 28. The golf ball of claim24, wherein the inner cover has an outer diameter of about 1.58 to about1.64 inches.
 29. The golf ball of claim 1, wherein the polyurethane isthermoplastic or thermoset.
 30. A golf ball comprising: a centercomprising a polybutadiene having a molecular weight of greater thanabout 300,000 and a resilience index of at least about 40; an outer corelayer surrounding the center, the outer core layer having an outerdiameter of at least about 1.51 inches; an inner cover layer surroundingthe outer core layer; and an outer cover layer disposed around the innercover layer, the outer cover layer comprising a polyurethane compositionformed from a prepolymer having less than 7.5 percent by weightunreacted isocyanate groups.
 31. The golf ball of claim 30, wherein theresilience index is greater than about
 50. 32. The golf ball of claim30, wherein the polyurethane composition comprises an isocyanate, atleast one polyol, and at least one curing agent.
 33. The golf ball ofclaim 32, wherein the isocyanate comprises 4,4′-diphenylmethanediisocyanate, polymeric 4,4′-diphenylmethane diisocyanate,carbodiimide-modified liquid 4,4′-diphenylmethane diisocyanate,4,4′-dicyclohexylmethane diisocyanate, p-phenylene diisocyanate, toluenediisocyanate, isophoronediisocyanate, p-methylxylene diisocyanate,m-methylxylene diisocyanate, o-methylxylene diisocyanate, or a mixturethereof.
 34. The golf ball of claim 32, wherein the at least one polyolcomprises a polyether polyol, hydroxy-terminated polybutadiene,polyester polyol, polycaprolactone polyol, polycarbonate polyol, ormixtures thereof.
 35. The golf ball of claim 32, wherein the curingagent comprises a polyamine curing agent, a polyol curing agent, or amixture thereof.
 36. The golf ball of claim 35, wherein the curing agentis a polyamine curing agent comprising3,5-dimethylthio-2,4-toluenediamine, or an isomer thereof;3,5-diethyltoluene-2,4-diamine, or an and isomer thereof;4,4′-bis-(sec-butylamino)-diphenylmethane;1,4-bis-(sec-butylamino)-benzene, 4,4′-methylene-bis-(2-chloroaniline);4,4′-methylene-bis-(3-chloro-2,6-diethylaniline); trimethyleneglycol-di-p-aminobenzoate; polytetramethyleneoxide-di-p-aminobenzoate;N,N′-dialkyldiamino diphenyl methane; p,p′-methylene dianiline;m-phenylenediamine; 4,4′-methylene-bis-(2-chloroaniline);4,4′-methylene-bis-(2,6-diethylaniline);4,4′-diamino-3,3′-diethyl-5,5′-dimethyl diphenylmethane;2,2′,3,3′-tetrachloro diamino diphenylmethane;4,4′-methylene-bis-(3-chloro-2,6-diethylaniline); or mixtures thereof.37. The golf ball of claim 35, wherein the curing agent is a polyolcuring agent comprising ethylene glycol; diethylene glycol; polyethyleneglycol; propylene glycol; polypropylene glycol; lower molecular weightpolytetramethylene ether glycol; 1,3-bis(2-hydroxyethoxy)benzene;1,3-bis-[2-(2-hydroxyethoxy)ethoxy]benzene;1,3-bis-(2-[2-(2-hydroxyethoxy)ethoxy]ethoxy}benzene; 1,4-butanediol;1,5-pentanediol; 1,6-hexanediol; resorcinol-di-(-hydroxyethyl)ether;hydroquinone-di-(hydroxyethyl)ether; trimethylol propane, or mixturesthereof.
 38. The golf ball of claim 30, wherein the prepolymer has fromabout 2.5 percent up to 7.5 percent by weight unreacted isocyanategroups.
 39. The golf ball of claim 30, wherein at least one of the innerand outer cover layers has a thickness of less than about 0.05 inches.40. The golf ball of claim 30, wherein the center has a Mooney viscosityof from about 40 to about
 80. 41. The golfball of claim 30, wherein thepolybutadiene has a vinyl-isomer content of less than about 2 percent byweight.
 42. The golf ball of claim 30, wherein the polybutadiene has acis-isomer content of at least about 95 percent by weight.
 43. The golfball of claim 30, wherein the center has an outer diameter of no greaterthan about 1.55 inches.
 44. The golf ball of claim 30, wherein thecenter comprises a material formed from a conversion reaction ofpolybutadiene having a first amount of trans-isomer, a free radicalsource, and at least one cis-to-trans catalyst.
 45. The golf ball ofclaim 44, wherein the reaction occurs at a temperature sufficient toform a polybutadiene reaction product having a second amount oftrans-isomer greater than the first amount of trans-isomer.
 46. The golfball of claim 44, wherein the cis-to-trans catalyst further comprises atleast one of an organosulfur compound, an inorganic sulfur compound, anaromatic organometallic compound, a metal-organosulfur compound,tellurium, selenium, elemental sulfur, a polymeric sulfur, or anaromatic organic compound.
 47. The golf ball of claim 46, wherein theorganosulfur component comprises at least one of 4,4′-diphenyldisulfide, 4,4′-ditolyl disulfide, or 2,2′-benzamido diphenyl disulfide.48. The golf ball of claim 44, wherein the cis-to-trans catalyst ispresent in an amount from about 0.1 to 10 parts per hundred ofpolybutadiene.
 49. The golf ball of claim 30, wherein the inner coverlayer comprises an ionomer resin, a polyurethane, a polyetherester, apolyetheramide, a polyester, a dynamically vulcanized elastomer, afunctionalized styrenebutadiene elastomer, a metallocene polymer, nylon,acrylonitrile butadiene-styrene copolymer or blends thereof.
 50. Thegolf ball of claim 30, wherein the inner cover has an outer diameter ofat least about 1.55 inches.
 51. The golf ball of claim 50, wherein theinner cover has an outer diameter of about 1.58 to about 1.64 inches.52. The golf ball of claim 30, wherein the polyurethane is thermoplasticor thermoset.
 53. A golf ball comprising: a center formed of apolybutadiene having a molecular weight of greater than about 300,000and a resilience index of at least about 40; an outer core layersurrounding the center, the outer core layer having an outer diameter ofat least about 1.51 inches; an inner cover layer surrounding the outercore layer, the inner cover layer comprising a polyurethane; and anouter cover layer disposed around the inner cover layer, the outer coverlayer comprising an ionomer or an elastomeric material.
 54. A golf ballcomprising: a center comprising a polybutadiene having a molecularweight of greater than about 300,000 and a resilience index of at leastabout 40; an outer core layer surrounding the center, the outer corelayer having an outer diameter of at least about 1.51 inches; an innercover layer surrounding the outer core layer; and an outer cover layerdisposed around the inner cover layer; wherein the inner and outer coverlayers are each formed of a polyurethane composition.